If a third (or a large number) of angels rebelled, what was the justification?

What was the justification of angelic rebellion?

You suggested that the creation of mankind was a factor, that

... their creation and future/destiny stir some resentment among the angels and their bright place, to the extent that the angels questioned his decision making?

My guess is that you heard a rumor circling around that was actually based on a Second Temple period speculation (period between Malachi and the birth of Jesus) culminating in a Jewish / Christian apocryphal composition known as The Life of Adam and Eve (c. 100-300 CE) and became part of the Islamic tradition attested even in the Qur'an.

That the justification was Satan's refusal to worship Adam is discussed in a paper published in Volume 113 of the Brill series Studies on the Texts of the Desert of Judah The book series is dedicated for

Scholarly translation and evaluation of Biblical texts from the papyri and manuscripts of Wadi Qumran and the Dead Sea Scrolls, and related bibliographic, linguistic, cultural and historical aspects of ancient Judaism and early Christianity.

The paper is Satan’s Refusal to Worship Adam: A Jewish Motif and Its Reception in Syriac Christian Tradition by Sergey Minov. The paper concentrates on the 2nd of these 2 group of explanations of the

why and how Satan, created originally as good, became quite the opposite -- a quintessential and paradigmatic enemy of the omnipotent and good deity, and of humanity.

First group:

stories in which Satan forfeits his original quality of goodness because he tries to challenge God himself and usurp his place in heaven;

Second group:

stories in which he loses his exalted status because of his enmity towards the primeval humans, God’s creatures.

Sub-motifs of the second group:

1) the veneration of the newly created Adam by the angelic forces; and 2) the refusal of Satan to participate in this act, which results in his rejection by God. One of the earliest attestations of this interpretation of Satan’s demotion comes from the apocryphal composition known as the Life of Adam and Eve.

The paper's investigation has 2 sections:

In the first part of my investigation, I discuss the account of the fall of Satan as it is presented in the Life. The main thrust of this discussion is that this interpretation of Satan’s fall is deeply rooted in the context of ancient Jewish speculation on the figure of Adam; I argue that this account took its point of departure from a Jewish tradition about the veneration of Adam by the angels. This latter tradition is itself attested in such diverse sources as the Slavonic apocryphon 2 Enoch and some rabbinic texts.

In the second section I offer an overview of the reception history of this originally Jewish tradition in the Syriac Christian milieu, from its earliest appearance during late antiquity, in the sixth-century composition known as the Cave of Treasures, until the early modern period. In the process, I explore how this tradition was adapted to and functioned within a wide range of literary genres and rhetorical settings. I place particular emphasis on how this tradition became an important topic of the Christian dialogue with Islam, in the context of the complex cross-cultural exchange that characterized societies of the medieval Near East. Because this explanation of Satan’s fall gained canonical status in the Muslim tradition, where it appears already in the Qurʾān, some later Syriac-speaking Christians began to perceive it as problematic and tried to marginalize it; those who continued to use this tradition also mobilized it for the purpose of polemic against Islam. I connect the diversity among Syriac-speaking Christians in the usage of this account with its popularity as an element of the mythological discourse that was shared by many groups across the Islamicate world: a world which was shaped by the tradition of the dominant Muslim majority, but was open to a certain degree to the participation of various religious minorities.

Conclusion

The Bible is silent on why angels rebelled, and it is understandable that the Jewish people, whose canonized Hebrew Bible was also missing the explanation, then speculated on a connection with Adam during the Second Temple period. This speculation was carried on through hundreds of years culminating in an official Islamic teaching recorded in the Qur'an BUT remains apocryphal from Christian point of view.

The Conclusion of the paper provides 2 reasons why, up to this day, this speculation (despite the popularity of the story among small minority subgroups of Christians) didn't become part of "orthodoxy" in any of the 3 mainstream Christian traditions, not even among the primary carrier of this myth, namely the Syriac-speaking Christians. Quote from the Conclusion section (emphasis mine):

Although this interpretation of the fall of Satan was marginalized in the tradition of rabbinic Judaism, early Christianity turned out to be particularly receptive to it, and constituted the primary channel of its transmission during late antiquity. It was through the mediation of Christians, most likely Syriac-speaking ones, that this myth became an integral part of the demonological tradition of Islam, where its popularity reached new peaks.

... It should be emphasized, however, that even among Syriac-speaking Christians this account did not become the par excellence explanation of Satan’s fall. One may propose several reasons for this. First of all, the fact of the appearance of this tradition in the Cave of Treasures, a work of doubtful pedigree in the eyes of at least some Syriac Christian theologians, might have negatively affected the perceived “orthodoxy” of this tradition. Second, as I have demonstrated above, the central place of this myth in the Muslim tradition could also have rendered it unacceptable to some Syriac-speaking Christians, especially those concerned with drawing clear boundaries between the two communities of faith. ...

The Bible describes the essential factors in Lucifer's fall. Lucifer could have stayed in favor with God, loved and honored by all the angels, exercising his God-given abilities to bless others and to honor his Maker. But the prophet writes:

Thine heart was lifted up because of thy beauty, thou hast corrupted thy wisdom by reason of thy brightness. (Ezekiel 28:17, KJV).

Little by little, Lucifer came to indulge a desire for self-exaltation.

...Thou hast set thine heart as the heart of God. (Ezekiel 28:6, KJV)

Thou hast said, ... I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation....I will ascend above the heights of the clouds; I will be like the Most High. (Isaiah 14:13, 14, KJV)

Instead of making God supreme and lifting Him up as deserving of the allegiance of His creatures, it was Lucifer's desire to win their hearts and their worship to himself. Coveting the honor which the infinite Father had given His Son, this prince of angels aspired to the position which only Christ should hold.

There is no excuse for sin; there can never be. Yet before sin had occurred the first time, they were ignorant of it and knew nothing of its baleful harvest. Perhaps, had they seen the end from the beginning, they would never have sinned. But for this reason, Christ tried to explain to them what would result, beginning with Lucifer. Lucifer, almost persuaded, continued in his course of rebellion on account of foolish pride. He could not admit, before all of the other angels, that he had been wrong. When the facts of the matter were laid open to their understanding, and all were given a chance to choose sides--whether for Lucifer, or for Christ--the battle lines were drawn.

⁷ And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels, ⁸ And prevailed not; neither was their place found any more in heaven. ⁹ And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him. (Revelation 12:7-9, KJV)

The next verse shows what Lucifer/Satan had been doing up to that point in time.

And I heard a loud voice saying in heaven, Now is come salvation, and strength, and the kingdom of our God, and the power of his Christ: for the accuser of our brethren is cast down, which accused them before our God day and night. (Revelation 12:10, KJV)

God's inclusion of Christ in the divine council which laid plans for the creation of our earth seems to have precipitated Lucifer's initial jealousies. He had already begun to think of himself more highly than he ought, and saw himself as equal to Christ. He wondered why he should not be allowed to join in that council. But no, it was only Christ who was allowed: the Father and the Son were together in the planning.

Conclusion

There was no justification for the rebellion, but having become proud, Lucifer, jealous of Christ's higher position, alleged that God's law was not fair. This has been his claim ever since, even to our day. It was this claim which gave rise to doubts in God's loyal subjects that must be given time to disprove. Our planet has become the experiment for sin, with all of the watching universe looking to see whether Satan's claims are justified or meritless. We are very near the point where no shadow of doubt remains and the experiment will be over--God the decided victor in the controversy.

If a third (or a large number) of angels rebelled, what was the justification?

We know not the exact moment the angels were created, but we know that they were created naturally good. Although, at the moment of their creation, they did not enjoy the Beatific Vision, for this is reserved for the Holy Angels who never sinned or rebelled against God.

The angels at the moment of their creation were in heaven that is to say the immediate atmosphere that surrounds the earth and the entire external physical universe. They were not in the intimate presence of God in Heaven.

St. Thomas Aquinas as well as others believe the sin of the fallen angels was one of pride and envy.

Sin can exist in a subject in two ways: first of all by actual guilt, and secondly by affection. As to guilt, all sins are in the demons; since by leading men to sin they incur the guilt of all sins. But as to affection only those sins can be in the demons which can belong to a spiritual nature. Now a spiritual nature cannot be affected by such pleasures as appertain to bodies, but only by such as are in keeping with spiritual things; because nothing is affected except with regard to something which is in some way suited to its nature. But there can be no sin when anyone is incited to good of the spiritual order; unless in such affection the rule of the superior be not kept. Such is precisely the sin of pride — not to be subject to a superior when subjection is due. Consequently the first sin of the angel can be none other than pride.

Yet, as a consequence, it was possible for envy also to be in them, since for the appetite to tend to the desire of something involves on its part resistance to anything contrary. Now the envious man repines over the good possessed by another, inasmuch as he deems his neighbor's good to be a hindrance to his own. But another's good could not be deemed a hindrance to the good coveted by the wicked angel, except inasmuch as he coveted a singular excellence, which would cease to be singular because of the excellence of some other. So, after the sin of pride, there followed the evil of envy in the sinning angel, whereby he grieved over man's good, and also over the Divine excellence, according as against the devil's will God makes use of man for the Divine glory. - Whether only the sin of pride and envy can exist in an angel?

Thus it seems that most probably Satan sinned immediately after his own creation and there was no interval of time in his decision.

There is a twofold opinion on this point. But the more probable one, which is also more in harmony with the teachings of the Saints, is that the devil sinned at once after the first instant of his creation. This must be maintained if it be held that he elicited an act of free-will in the first instant of his creation, and that he was created in grace; as we have said (I:62:3. For since the angels attain beatitude by one meritorious act, as was said above (I:62:5), if the devil, created in grace, merited in the first instant, he would at once have received beatitude after that first instant, if he had not placed an impediment by sinning.

If, however, it be contended that the angel was not created in grace, or that he could not elicit an act of free-will in the first instant, then there is nothing to prevent some interval being interposed between his creation and fall. - Whether there was any interval between the creation and the fall of the angel?

As to the exact sin of the fallen angels, it seems most probable that they desired to be as God. This can be seen in the very beginning in Genesis when the Deceiver lied to Eve in the Garden of Eden.

The serpent’s deception in the Garden had included a grain of truth. Satan told Eve, “God knows that when you eat from it your eyes will be opened, and you will be like God, knowing good and evil” (Genesis 3:5). What the serpent did not say was that knowing evil would damage Adam and Eve’s relationship with God. Half-truths can be as deceptive as full-blown lies. - How did the knowledge of good and evil make man like God (Genesis 3:22)?

Again this desire to be as God is echoed in the writings of Thomas Aquinas and the the sin of highest angel could be the cause of the angels to follow in kind.

The sin of the highest angel was the cause of the others sinning; not as compelling them, but as inducing them by a kind of exhortation. A token thereof appears in this, that all the demons are subjects of that highest one; as is evident from our Lord's words: "Go [Vulg. 'Depart from Me'], you cursed, into everlasting fire, which was prepared for the devil and his angels" (Matthew 25:41). For the order of Divine justice exacts that whosoever consents to another's evil suggestion, shall be subjected to him in his punishment; according to (2 Peter 2:19): "By whom a man is overcome, of the same also he is the slave." - Whether the sin of the highest angel was the cause of the others sinning?

Some theologians postulate that the pride that caused the sin of the fallen angels was due to the incarnation of Christ. They refused to serve beings of an inferior nature!

It is the non serviam of Satan that messed up everything at the demonic rebellion against God.

Although nothing definite can be known as to the precise nature of the probation of the angels and the manner in which many of them fell, many theologians have conjectured, with some show of probability, that the mystery of the Divine Incarnation was revealed to them, that they saw that a nature lower than their own was to be hypostatically united to the Person of God the Son, and that all the hierarchy of heaven must bow in adoration before the majesty of the Incarnate Word; and this, it is supposed, was the occasion of the pride of Lucifer (cf. Suarez, De Angelis, lib. VII, xiii). As might be expected, the advocates of this view seek support in certain passages of Scripture, notably in the words of the Psalmist as they are cited in the Epistle to the Hebrews: "And again, when he bringeth in the first-begotten into the world, he saith: And let all the angels of God adore Him" (Hebrews 1:6; Psalm 96:7). And if the twelfth chapter of the Apocalypse may be taken to refer, at least in a secondary sense, to the original fall of the angels, it may seem somewhat significant that it opens with the vision of the Woman and her Child. But this interpretation is by no means certain, for the text in Hebrews 1, may be referred to the second coming of Christ, and much the same may be said of the passage in the Apocalypse.

It would seem that this account of the trial of the angels is more in accordance with what is known as the Scotist doctrine on the motives of the Incarnation than with the Thomist view, that the Incarnation was occasioned by the sin of our first parents. For since the sin itself was committed at the instigation of Satan, it presupposes the fall of the angels. How, then, could Satan's probation consist in the fore-knowledge of that which would, ex hypothesi, only come to pass in the event of his fall? In the same way it would seem that the aforesaid theory is incompatible with another opinion held by some old theologians, to wit, that men were created to fill up the gaps in the ranks of the angels. For this again supposes that if no angels had sinned no men would have been made, and in consequence there would have been no union of the Divine Person with a nature lower than the angels. - Devil