Does the phrasing in Nicene Creed cast doubt on the eternality of The Son of God?

The Creed of Nicaea starts with a declaration of belief "in one God, the Father, Almighty, maker of all things visible and invisible" then expresses belief in the one Lord, Jesus Christ [see 1 Corinthians 8:6] before stating belief in the Holy Spirit.

Of Christ, the Creed says that he is "only-begotten, that is, from the substance of the Father: God from God, Light from Light, Very God from Very God, begotten not made, of one substance with the Father, through whom all things were made, both in heaven and on earth..." and so on.

So far, there is nothing that even hints at doubt as to the eternality of the Son. However, you say that being 'of or from God indicates a beginning', which may show a lack of understand of what the Creed means. This may be due to having a modern, English-language view of what 'only-begotten' means, and fails to grasp the koine Greek words used in the Bible that deal with this. Rather than delve into details about that, let me quote this book to show the problems being dealt with, leading up to the Creed using those phrases.

"To exclude Arian error, the Council produced its own creed [which I give some details of above]...

Apparently Arius could agree to any statement using solely biblical language. Constantine supported the introduction of the word 'consubstantial' - probably suggested by a Western bishop.

'Consubstantial' (h*m*ousios) had been introduced to Christian theology by Gnostics who believed that the heavenly powers shared in the divine fullness. Similarly Origen probably applied it to the Son as a true offspring of the Father, but later bishops had been unhappy about its implications. For many at Nicaea it probably implied that the Son was no less divine than the Father; that the two were equally divine, as an earthly father and son are equally human. For the Westerners and a few Easterners, Alexander and Athanasius, his personal assistant, Eustathius of Antioch and Marcellus of Ancyra, it meant that Father and Son were one in a single Godhead. Both these senses ruled out Arian misconceptions..." The History of Christianity, pp.158-9, Lion, 1985

Now, seeing the background to this Creed, it can be understood why it then went on to state:

"And those who say: 'There was a time when he was not', and: 'Before he was begotten he was not', and: 'He came into being from nothing', or those who pretend that the Son of God is 'Of another substance, or essence', or 'created' or 'alterable' or 'mutable', the catholic and apostolic church places under a curse." (Ibid. p159) Emphasis mine

Because of all the semantics tricks played by Arius and those sympathetic to him, that creed had to make those detailed statements, followed with anathemas against those who believed as Arius believed. Arius believed there was a time when the Son did not exist, being created at a point in time by the Father, and that he was actually an angel.

Now that this has been made clear, it can be seen that the Creed of Nicaea is diametrically opposed to any notion of the Son of God (also known as the Word of God, John 1:1-14) not being eternal, as the Father is eternal. A main purpose of the Creed was to make it impossible for those (like Arius) who did believe the Son was created, that the Son was not eternal, to hold any office in the Christian church.

The creed explicitly denounces “those who say: 'There was a time when he was not;' and 'He was not before he was made.” In other words, according to the creed, He always existed.

The creed also says that “By whom (Jesus Christ) all things were made both in heaven and on earth.” “All things,” therefore, presumably refers to this entire universe. Space, time and matter defines the universe. By implication, even time was created “by” Jesus Christ, as amazing as that may sound. Again, the conclusion is that He always existed. There was no time that He did not exist.

Θεὸν ἐκ Θεοῦ (theos from theos or god from god), is an interpretation of the description in the Creed of Christ as “begotten” (born). Since He is metaphysically “born” from God, He came out of the being of God and is in a different category relative to created things.

And, as the creed indicates, He is the “only-begotten.” In other words, He is the only one that was ever came out of the being of God.

But then, your question is, how do we reconcile the fact that He always existed with the fact that He was born of God, which implies a beginning? I propose that we explain this by making a distinction between our universe of time, space and matter, and the True Reality, which exists beyond our universe, but from where the power and intelligence came that produced our universe:

Time exists in our universe and Christ existed for all that time, but that time began 13 billion years ago with the big bang.

But in that True but incomprehensible Reality, arguably, time does not exist. In that reality, the Son was born from the being of God, but since time does not exist, there is no before or after and the word “always” does not apply for the word “always” is only valid where time exists.

From implies source or origin, not necessarily a temporal change. The phrasing God of God was meant to define the relationship of Son to God the Father; they both are one substance.

Note that the Creed further says "born of the Father before all worlds/ages" which also indicates an eternity to the Son being begotten

The Nicene Creed conveys an eternal begetting - the only begotten Son.

This begetting is not a matter of time, it is a matter of eternity. (Which is not 'a long period of time' it is another state altogether - an eternal state.)

'In the beginning was the Word' conveys that when the beginning began, the Person who incorporates, within himself, the concept of 'Word' (the sum of all that can be intelligently communicated) already was, in existence.

The Son is not 'made'. He is begotten. And he is the only begotten Son of God.

There is a plurality - 'sons of God' - in regard to creation and these we see in Job. They are created beings.

There is also a plurality - 'sons of God' - in regard to redemption, by new birth, in a New Testament and in a New Creation.

But none of the 'sons of God' - by creation or by redemption - is ever referred to as 'the son of God'.

When the singular is used, with an article, it is clear that there is a personal singularity which refers only to one person - the Son of God, Jesus Christ.

His existence did not begin with the beginning. In the beginning was the Word.

The extensive writings of, for example, Athanasius, at the time of the Council of Nicea, clearly indicate the concept of eternal begetting. And also the concept of duality of nature : that Jesus Christ joins in his Person all the attributes of Divine nature and all the attributes of human nature.

These two natures do not converge or mingle or merge : they are two distinct things. They meet in the Person of Jesus Christ.