Trinitarians place heavy emphasis on the idea that Jesus, the Son of God, is “co-eternal” with God his Father. What is meant by this is not simply that Jesus is eternal in the sense that he is everlasting and will live forever, as God his Father does, for this is a point upon which Trinitarians and Unitarians agree. Rather the emphasis of trinitarians on this point is that the Son is co-eternal with the Father in the sense that He is co-eval with Him; that as long as God has existed (which is always, and without beginning) the Son has existed as well.
This doctrine of past co-eternality, or coevality (that the Son is as old as the Father) is never stated in the Bible. Common texts alleged in support of the doctrine do not state it directly, but are rather the subject of argument by inference. Ultimately the philosophical and doctrinal presuppositions about time a person brings to these biblical texts will significantly affect their reading of the various passages alleged in favor of co-eternality. But to understand whether or not the Son is co-eternal with the Father, do we really need to dive deep into speculation about the nature of time? Or does the Bible actually provide us with clear answers?
While the Bible never expressly teaches ‘co-eternality’, it does, to the surprise of some, say things that are incompatible with it. Firstly, a text commonly noted by opponents of co-eternality is 1 Chronicles 17:13:
“I will be his father and he shall be My son”
This text in which God speaks to King David has often been taken as a Messianic text, having not only reference to Solomon, David’s immediate heir, but also to the future Christ, the Son of David, who would sit on David’s throne forever in God’s kingdom. Notice that God did not say that He already was the Father of David’s son, but that He “will be” Father to David’s descendant in the future; likewise, the Messiah is not presently said to be God’s son, but it is promised that he “shall be My son” in the future. If Jesus already existed at this time in history as God’s co-eternal Son, it seems very strange indeed that this relationship is spoken of only as something to come in the future and not something which existed at present.
There is another passage which is even clearer than this at dispelling the notion that Christ is co-eval with the Father, 1 Peter 1:20:
For He [Christ] was foreknown before the foundation of the world, but has appeared in these last times for the sake of you who through Him are believers in God, who raised Him from the dead and gave Him glory, so that your faith and hope are in God.1 Peter 1:20-21 NASB
This one verse disproves the theory that the Son is coeval with the Father; for to foreknow (or foreordain) is to know (or ordain) beforehand; and so if God foreknew His Christ, of necessity He must have been before Christ. If Christ had eternally pre-existed with God, then it would not be said that God foreknew Christ, but simply that He knew him.
It is, then, a necessary implication of this text that God was before His Christ, and therefore, that Christ was after his Father -or else it would not be possible for Peter to have said that God foreknew Christ. Again, were Christ co-eternal with the Father as trinitarians say, this passage would not say that Jesus was foreknown by God, but simply that God knew Him. But by saying that God foreknew Christ, Peter puts God chronologically before Christ.
Its a great blessing that the Bible actually supplies us an answer to the otherwise highly philosophical and speculative question of co-eternality. No amount of extra-biblical philosophical speculation or human tradition can compare to the witness of the Bible itself. The apostle Peter was clear: God foreknew Christ before the foundation of the world, and so it necessarily follows from this that the Father is before Christ, and that Christ is after the Father, not co-eternal or coeval with Him.
We might end by noting that the amount of weight trinitarians place upon the doctrine of co-eternality is downright dangerous- they declare that a person is anathema (accursed) and excommunicate from the body of Christ if they do not agree that the Son is co-eternal with the Father, all while this doctrine is not only absent from the Bible itself, but actually opposed to its teaching. Is the apostle Peter anathema? The modern Christian must judge if they will be better served to side with the beloved disciple of the Lord Jesus, or the council of Nicea on this matter.