What is the Christological difference between the early Church fathers and the Arians?

It is an error to believe Arius popped out of a vacuum to teach his heresy. He didn't. Most do not know the background that began about 130 years prior to Nicea. If you understand the background, then you will understand the argument.

Arius taught that there was a time when Christ did not exist. He taught Christ was a creature, rather than Creator. In contrast, Nicea would teach that Christ is very God of very God. Those were the two choices.

Arius as it turns out was walking in the footsteps of Lucian of Antioch who was following in the footsteps of Paul of Samasoto.

So far we have these three men following the same idea of some form of adoptionism. Adoptionism is the idea, again, that Christ is a creature, either a good man who became god-like, or became god at his baptism, or something similar.

Now, the question is were they following anyone? The answer is yes. They were following Theodotus of Byzantium. He is the source for Arius' ideas. As Wiki confirms, the first known proponent of adoptionism was Theodotus.

The next question is how did adoptionism find its way into the Church? The answer is persecution.

. Hippolytus stated that Theodotus was a native of Byzantium, who denied Christ in time of persecution—a fact which accounted for his heresy, since he could thus maintain that he had only denied man, not God. -source-

So, yes there was "arianism" before it became known from Arius, its champion. It has a history and it sources to an important person at the time who because of persecution denied Christ. Because of that, including the full implication of God the Son, he invented the adoption theory. Thus he could deny that he denied God, but only a man.

The earlier fathers did sometimes make statements that later came to be recognized as formally heretical. But since no one called them on those statements during their lifetimes, we didn't get to see the debate play out. They didn't have a chance to say, "Oh yeah... good point," and explain, revise or qualify their statements. And on the negative side, they didn't have a chance to say, "Yes, that is what I mean. The Son is a creature!" So later generations give them the benefit of the doubt and interpret their language the way they believe the saint himself would have, if he'd had a reason to revisit it in his own lifetime. Only God knows if he really would have, of course, but it's obviously the right way to treat your father.

In the middle of the first volume of his five voluminous work on the history of Christian theology, as a Lutheran historian Jaroslav Pelikan writes,

The truth, even the truth of the Gospels, is never pure and clear, and rarely simple.

Jaroslav Pelikan, The Emergence of the Catholic Tradition, vol. 1, Chicago: University of Chicago Press, 1971, p. 266.

It is simply impossible and beyond description to be able to explain the Trinity unequivocally says a Calvinist Millard Erickson,

He are three and they is one.

Millard Erickson, God in Three Persons, 1995, p. 270.

There is an open debate whether or not precursor to Arianism predate Nicene council. This answer will not address that debate but rather focusing on Ante Nicene Fathers' Trinitarianism to understand their differences when being compared with Arianism in terms of their Christology.

To help us grasp the context of Trinitarian development prior to Nicaea, let us briefly go through three Trinitarian traditions:

Roman Angelic Christology: The Messenger and the Message

St. Justin Martyr is recognized as “the most important of the Greek apologists of the second century and one of the noblest personalities of early Christian literature.” ¹ Following Angelic Christology as commonly held among Early Christian and Second Temple Jewish literatures, he wrote,

I consider it necessary to repeat to you the words which narrate how He who is both Angel and God and Lord, and who appeared as a man to Abraham, and who wrestled in human form with Jacob, was seen by him when he fled from his brother Esau.

Justin, Dialogue with Trypho, 58.

His Angelic Christology plays a fundamental role in his interpretation of the OT and in his Angelic Logos view. In terms of Justin’s conceptual framework, his use of the title Angel complement the title Logos and the Logos Christology for which he is famous. Justin’s use of the title Angel as a Christological title, based on the similarity of both title and function, is to show that Christ is the Angel of the Lord who appears throughout the OT (e.g., to Abraham in Genesis 15–22; to Jacob in Genesis 28–35; to Moses in Exodus 3; and to Joshua in Joshua 5–6). The Messenger is the Message Himself. He anticipated St. Augustine's notion that the OT is the new concealed and the NT is the old revealed.²

I shall attempt to persuade you, since you have understood the Scriptures, [of the truth] of what I say, that there is, and that there is said to be, another God and Lord subject to the Maker of all things; who is also called an Angel, because He announces to men whatsoever the Maker of all things—above whom there is no other God—wishes to announce to them.

Justin, Dialogue With Trypho, 56.

This Patristic Angelic Christology should not be confused with John Calvin's view on Christ-Michael theory or Seven Day Adventist belief that the Archangel Michael is the Second Person of the Holy Trinity. Because the Church Fathers never conflate Michael with the Angel of the Lord; the two are distinct, the former an angel by nature while the later by voluntary condescension.

Our teacher of these things is Jesus Christ, who also was born for this purpose, and was crucified under Pontius Pilate, procurator of Judaea, in the times of Tiberius Caesar; and that we reasonably worship Him, having learned that He is the Son of the true God Himself, and holding Him in the second place, and the prophetic Spirit in the third, we will prove. For they proclaim our madness to consist in this, that we give to a crucified man a place second to the unchangeable and eternal God, the Creator of all; for they do not discern the mystery that is herein, to which, as we make it plain to you, we pray you to give heed.

Justin, The First Apology, 13.

Justin did not actually use the exact phrase second God (δεύτερος θεός) in reference to Jesus. However, he did use a couple of equivalents such as another God and Lord (Θεός και Κύριος έτερος) and referring to Him who is caused by the uncaused as a second place (δεύτερα χώρα).

God [is] the cause of His power and of His being Lord and God.

Justin, Dialogue with Trypho, 129.

For Justin, the uncaused is the cause of the second divine person. This pre Nicene Angelic Logos view later reappeared during Arian controversy two centuries later.

Antiochene Logos Christology: The innate and the begotten Logos

St. Theophilus of Antioch was an important theologian and apologist in the early church. His work To Autolycus was widely read and referenced in the writings of St. Irenaeus of Lyon, Tertullian of Carthage, Novatian of Rome, Lactantius of Constantinople, and Eusebius of Caesarea. He is the first to use the word Trinity (τρίας) for the union of the three divine persons: “the three days, which were before the luminaries are types of the Trinity (τριάδος) of God and His Word (λόγος) and His Wisdom (σοφία).”³ There appears to have been a direct connection in the minds of the early Church fathers between the divine Counselor of Isa 9:6 and the plural pronouns of Gen 1:26. Theophilus, just prior to his use of the title Counselor, has stated that the “Let Us make” of Genesis was spoken by the Father “to none other than His own Logos and His own Sophia" who are his hands the agency through whom He creates.⁴ He anticipated Irenaeus on using the two hands of God as a metaphorical language.⁵

Theophilus is also the first to distinguish between the Logos ένδιάθετος and the Logos προφορικός—the Logos internal or innate in God and the Logos uttered or emitted by God. A distinction in a terminology, which will have an important role to play in the explication of later Trinitarian and Christological development during Arian controversy two centuries later. The Logos is both innate in the bowels of God and also distinct from God who begot Him before the creation, so that He might assist in it. God "having His own Logos internal—ένδιάθετον—begat Him, emitting—προφορικός—Him along with His own Wisdom before all things. He had His Logos as a Counselor in the things that were created by Him, and by Him He made all things.”⁶ Theophilus knows that the Logos is eternally pre-existent since God's Logos is always innate as the mind of God and constantly communicates with Him. “When God willed to make all that, He determined, He begot His Logos, uttered—προφορικοί—the firstborn of all creation, not Himself being emptied of the Logos but having begotten the Logos and always conversing with the Logos."⁷

The Son is Himself divine in nature; yet He remains distinct from God in person, i.e., the Logos is with God. In the divine economy it is the Son of God who becomes the Voice⁸ and the Letter of the Father sent into the world to be heard and seen by men. Theophilus calls the spoken Logos Son because He is the firstborn of creation.⁷ He is the theophanic presence of His Father: The begotten Logos is the face of God, the exact icon of God's subsistence (ὑπόστασις).⁹ As God's right hand He "assuming the person of the Father and Lord of all, went to the garden in the face of God, and conversed with Adam."⁷ At that time it's Orthodox to see the Trinitarian distinction sharing the same subsistent.¹⁰ Before later at Council in Alexandria in 362 St. Athanasius of Alexandria began to clarify the difference between substance (οὐσίας) and subsistence (ὑποστάσεως) which then set a stage for Cappadocian Trinitarian and Christological development.

Referring to the Johannine Prologue he wrote, "[it shows] that at first God was alone, and the Logos [already exists] in Him. ... The Logos, then, being God, and being naturally produced from God, whenever the Father of the universe wills, He sends Him to any place; and He, coming, is both heard and seen, being sent by Him."⁷ This view later developed further by Ss. Lucian of Antioch and Dionysius of Alexandria. He is the Son who is sent into the world as a representative of His Father, to be "heard and seen."⁷ He is called God's servant,⁶ reflective of His work in the world He created on behalf of His Master.¹¹ This was an argument that the Arians later point to to show the antiquity of their argument, of the emanation of the spoken Logos "whenever the Father of the universe wills."⁷ Furthermore, Theophilus continues to point out that the begotten Logos "is called the Beginning because he leads and dominates everything fashioned through Him."⁶ Arius in his apologetic letter to Eusebius of Nicomedia refer to himself as a fellow Lucianist who was persecuted for preserving the faith of the Fathers.¹²

Alexandrian Sonship Christology: The eternal generation and subordination of the Son

St. Dionysius of Alexandria, a disciple of Origen, challenged Modalist h*m*ousion (όμοούσιον) language and excommunicated Sabellius at a council in Alexandria in 260-1. Sabellius' theology of the silent God (θεος σιωπών) as distinct from the speaking God (θεός λάλων) was condemned by championing Origen's eternal generation together with Theophilus' and Lucian's views that God is "always conversing with the Logos."⁷ The spoken Logos co-exist eternally with God as His innate Logos. Before He became the firstborn in creation "at first God was alone, with the Logos in Him."⁷ At no time God was alone without His innate Logos.

In challenging this Modalism Dionysius used language, which some suspected of being tainted with subordinationism. In the Latin West this term or more precisely its Latin analogue had been a common expression since Tertullian. Novatian wrote about a common substance—communio substantiae ad Patrem—in the Trinity. It was in this context that Pope of Rome St. Dionysius wrote against the Sabellians and rebuked the Metropolitan of Alexandria for not using the term one substance. He avoided the Greek term common substance (όμοούσια) because similarly another council at Antioch in 268-9 also had been condemned the h*m*ousion (όμοούσιον) language used by Samosatans.

The term consubstantial (όμοούσιος) was also used by the Gnostics in a usage, which clearly entailed emanation from the First Uncaused Cause. This explains the negative or cautious attitude that Origenists have toward the expressions one essence. He sent his letter to Council of Antioch in 268-9, convened to deliberate the theology of Paul of Samosata, rejected and condemned the term όμοούσια. It's in this context that he condemned the Samosatan term όμοούσια and talked of the Son as being generated or produced (ποιητά) from the Father following Theophilus, "being naturally produced from God."⁷ This exchange between the two bishops, Dionysius of Rome and Dionysius of Alexandria, foreshadows the coming Arian controversy 50 years later.

What is the difference between Ante Nicene Fathers and Anti Nicene Arians in terms of their Christology?

The word Logos as we know stands in Greek both for internal reason and external voice. Since the inward thought is immediately connected with and passes on into language-as its corresponding development-it was natural to consider the mental and vocal act as virtually one and the same. As the common term expressing them suggested, as if a thought were only an inchoate word, and a word only a spoken thought. Hence, came the innate (ένδιάθετος) and spoken (προφορικός) Logos, who thus both distinguished and identified thinking and speaking.

While Eunomius ... have shied ... from referring to the divinity of Jesus christ as divine "power," and earlier generation of anti-Nicene (including Arius and Asterius) was willing to allow that scriptural designation, provided that this christic "Power" and Logos was differentiated from the innate divine power and logos that was not hypostatic. These anti-Nicene ... acknowledge that God has a power intrinsic to his nature but not that this power is hypostatic.

Khaled Anatolios, Retrieving Nicaea: The Development and Meaning of Trinitarian Doctrine, Baker Academic: Grand Rapids, MI, 2011, p. 219. Emphasis by the author.

The term ύπόστάσις had been used in the past to distinguish the three in the Holy Trinity, especially by St. Hippolytus of Rome, Novatian, and Tertullian. For them, however, υπόστασις designated almost the same as ουσία, and they considered that as a synonym of the unity of essence. The term ύπόστάσις remained indistinct from the concept of essence and this is precisely why the terminology of Dionysius of Alexandria’s theology was so disturbing to the Latins. In general, until the middle of the fourth century substance (ουσία) and subsistence (ύπόστάσις) were interchangeable both as ideas and terms. St. Jerome in his letter to Pope St. Damasus bluntly writes that "the school of worldly science knew of no other meaning for the word subsistence than substance."¹³ In the anathemas pronounced by the Council of Nicaea ουσία and ύπόστάση are considered as identical.¹⁰

Later when the Fathers of the Council of Ancyra in 358 began to talk about three hypostases they were immediately accused of tritheism. Under the direction of Athanasius the Council of Alexandria in 362 declared that both forms of expression are compatible and have the same meaning. This, however, did not resolve the problem. Both terms had to be defined and established within an integral conceptual system. It was not possible to be satisfied with classical philosophical terminology because its vocabulary was insufficient for theology. Classical terms and concepts had to be reshaped. This task was undertaken by the Cappadocian Fathers a few decades later.

Following Justin, Theophilus, and Dionysius, Arius is famously known for saying,

There was once [the Son when He] was not—ήν ποτέ oτε ουκ ην.

Arius cited by Athanasius of Alexandria, Against the Arians, 3:61.

That statement when being compared with three Trinitarian traditions briefly outlined above apparently does not contradict one another. During Nicene council out of 320 bishops who attended, two refused to sign Nicene faith: Theonas of Marmarica and Secundus of Ptolemais. From 318 Nicene Fathers who signed the Nicene faith, three refused to excommunicate Arius: Theognis of Nicaea, Maris of Chalcedon, and Eusebius of Nicomedia. All five bishops were deposed and exiled together with Arius. Later the Church canonically exonerated and restored to their ecclesial ranks those three (who signed Nicene faith while refused to excommunicate Arius) together with Arius who then accepted Nicene terminology of consubstantial (όμοούσιος).¹⁴

In the recent decades there are many attempt to exonerate Arius. While we can find similarities between Arius and the Fathers prior to Nicaea, such that they all consider the Son receiving the essence from the Father and hence denying the Son as an autotheos (God in Himself). But in principle they're not on the same camp, because the former considered the Son's divinity which derived to be lesser in glory than the Father's divinity who has no origin of derivation. Despite the fact that many of the Church fathers prior to Nicaea like the Arians had no difficulty in affirming that the Logos is begotten by God's will¹⁵ to be His Son before time began. This is the principal issue that separate the Ante Nicene Fathers from the Anti Nicene Arians.

¹ J. Quasten, Patrology, 4 vols., Westminster, MD: Newman, 1962-86, 1:196.

² Augustine, A Treatise on the Spirit and the Letter, ch. 27.

³ Theophilus, Ad Autolycum, 2:15.

⁴ Theophilus, Ad Autolycum, 2:18.

⁵ Irenaeus, Against Heresies, 5:17.

⁶ Theophilus, Ad Autolycum, 2:10.

⁷ Theophilus, Ad Autolycum, 2:22.

⁸ J. H. Charlesworth, “The Jewish Roots of Christology: The Discovery of the Hypostatic Voice,” Scottish Journal of Theology 39 (1986) 19-41.

⁹ St. Paul, Epistle to the Hebrews 1:3.

¹⁰ At the Council of Nicaea in 325 there was a pronouncement of anathema declared at the end of the Creed to those who distinguish the substance or subsistent which later was revised at Council of Alexandria in 362. This is why Niceno-Constantinopolitan Creed omitted the anathemas in 381.

¹¹ A language later used by Dionysius of Alexandria to show subordination of the spoken Logos to His Master.

¹² Arius, Letter to Eusebius of Nicomedia, 319, cited by St. Theodoret of Cyrrhus, Ecclesiastical History, 1:4.

¹³ Jerome, Letter 15 to Pope Damasus.

¹⁴ Similar to Nestorius who later in his Bazaar of Heracleides explained that he holds no enmity regarding honoring the virgin Mary with the title of Theotokos like Theodore of Mopsuestia his teacher did but he was afraid that such terminology might revived Apollinarian Christology and shipwreck the whole Niceno-Constantinopolitan faith which Diodore of Tarsus worked so hard to preserve by distinguishing the two natures clearly. Arius likewise following Eusebius accepts Nicene όμοούσιος like St. Lucian and St. Dionysius before him. His concern was to combat Modalism by maintaining a clear distinction between the First Uncaused Cause who has no beginning and His spoken Logos who has a beginning begotten by the unbegotten.

¹⁵ During the Arian controversy, a new theological development was adopted where the internal processions within God in generation and spiration are considered not as an act of will but as an activity by nature. God by nature caused the Son's generation and the Holy Spirit's spiration. "What proceeds by nature from something is just like the thing from which it proceeds, but what proceeds from something by an act of the will is not of the same nature as that from which it proceeds but is as the one willing wishes it to be." St. Hilary, Categories 10.

First of all, there was no Arianism prior to Arius because Arianism started with Arius.Arius began to teach a new teaching. He taught that the Logos had a beginning of existence.Although some scholars like Alexander Vasiliev refers to Lucian as the Arius before Arius.This merely shows that Lucian hold onto a proto-Arianism (source).

Arius was condemned while Justin, Theophilus, Dionysius, and pre-Nicene Fathers were considered Orthodox because the former denied consubstantiality (oneness in essence) of the Father and the Son while the latter supported it.

In Dialogue with Trypho Ch. 128 , Justin Martyr said: “this power is indivisible and inseparable from the Father" and “begotten from the Father, by His power and will, but not by abscission, as if the essence of the Father were divided,”

The Alexandrian Dionysius used the term "same substance," but refused to rely on it theologically because the word was not used in any biblical text (source).

Theophilus of Antioch spoke of the Logos as begotten from the substance (ousia) of the Father (source).

Athenagoras ( A.D. 177) wrote:

"We acknowledge one God, uncreated, eternal, invisible, impassable [i.e., not subject to suffering], incomprehensible, illimitable … by whom the universe has been created through his Logos … We acknowledge also a Son of God. Nor let anyone think it ridiculous that God should have a Son … the Son of God is the Logos of the Father. If … it occurs to you to inquire what is meant by the Son, I will state briefly that he is the first product of the Father, not as having been brought into existence, for from the beginning God, who is the eternal mind, had theLogos in himself, being from eternity instinct with Logos. (Plea for the Christians ch. 10)

Some of the pre-nicene fathers were subordinationists yet they still adhere to Jesus as "God of God." Gregory Thaumaturgus, Irenaeus, Athenagoras and others taught that the Son is eternally begotten from the Father not created from nothing. On the other hand, Arius introduced a completely alien thought to the church by teaching that the Logos had a beginning of existence, created from nothing.