Trinitarians as well and Unitarians have historically agreed upon the fact that the Son of God is caused in some manner- the Nicene Creed itself declares that the Son is “begotten” of the Father. This belief is well-founded on both the basis of the Bible and reason.
Firstly, Jesus expressly owns that he has his life from his Father:
As the living Father sent Me, and I live because of the Father, so he who eats Me, he also will live because of Me.John 6:57 NASB
This is clearly acknowledging the Father as the one Who has given him life- and such necessarily involves the Father in some sense being the origin and cause of the Son. And while Jesus also acknowledges that he has “life in himself”, this too he acknowledges is not originally his, but has been given to him by his Father:
For just as the Father has life in Himself, even so He gave to the Son also to have life in Himself;John 5:26 NASB
In addition to these clear testimonies, we may note that the very name “son” ordinarily implies that the one bearing that name has been caused by their father. Of course, there are lots of exceptions to this, as in the case of adoption, or of simply speaking figuratively; but in the case of Jesus, we may not that he is called God’s “only-begotten Son”. That’s significant, because it tells us what sort of Son Jesus is to God- his sonship is not one of adoption or merely a figure of speech, but rather Jesus is God’s Son because he has been begotten by God.
Being begotten, of course, necessarily involves being caused by the one begetting. Bible-believing Trinitarians and Unitarians generally agree up to this point- again, the council of Nicea itself presents Jesus’s generation from the Father as having great theological significance. Where Trinitarians, Arians, and Biblical Unitarians disagree on this is on when Jesus was begotten, and what precisely this generation looked like. Was this an eternal necessary act of the Father? Does it signify ex-nihilo creation of the Son before the creation of the universe? Or does it pertain to Jesus’s conception in Mary by the Holy Spirit? We shall return to these questions below.
Before moving on, however, it is worth also addressing some of the logical reasons why its important to understand that Jesus is caused by the Father, even from a historic trinitarian perspective. Historically this has been seen as important in large part because this causal relationship clearly distinguishes the Father from the Son- the one Who causes and the one who is caused, are necessarily two distinct persons. Also, we may again note that this is the foundation for the highly significant father-son relation that the Bible presents Jesus as having with God. But its also worth noting that the idea that the Son is uncaused would present something of a theological nightmare -and this is something modern evangelicals, who seem quick to throw off the historic trinitarian confession that the Son is caused by the Father, should take to heart.
The problem resulting from an uncaused Son is this: if the Son is not caused by the Father, then firstly, that he is really a distinct person besides the Father is thrown into doubt. If Jesus is not caused, only two options exist: either he is a distinct uncaused entity besides the Father, and so there are two uncaused entities, which would effectively be to assert that there are two Gods, or else, if it is maintained that there is only one uncaused entity (and so only one God), then Jesus will necessarily be one and the same with the uncaused Father, and there will be no real Father-Son distinction at all. That is to say, if one asserts that the Son is uncaused, the only two options that are open to that person are polytheism and modalism- either Jesus becomes as second first principle of the universe, a second uncaused cause of all things in addition to the Father, or else he will necessarily be uncaused simply by being the Father Himself.
These significant theological problems seem to be ignored by many modern Christians, but have historically factored into creedal and confessional trinitarianism, like Arianism and Unitarianism, teaching that the Son is in some manner caused by the Father.
We now return to the above question of the time and manner of Jesus’s origination from God. We have seen above that Jesus professes himself to have his life from the Father, and that he is God’s Son, not merely in name or by adoption, but as having been begotten by God. But when was Jesus’s origin from God? And what was the manner of his generation from the Father? As be have addressed above, Trinitarians, Arians, and Biblical Unitarians all answer this question significantly differently, and so, the answers have been a matter of no small debate.
In the midst of these intense debates, I will suggest that mere theological speculation has been relied upon too much, and the Bible too little. It may come as a shock to the reader to learn that the Bible actually professes to give us an account of Jesus’s origin:
Now the [origin, genesis] of Jesus Christ was as follows: when His mother Mary had been betrothed to Joseph, before they came together she was found to be with child by the Holy Spirit.Matthew 1:18, NASB
Matthew goes on in the following several verses to recount in summary the story of Jesus’s conception in the virgin Mary, and subsequent virgin birth. Its extremely noteworthy here that the crucial word in 18a, typically translated into English as “birth” or “generation”, is actually not the Greek word for either, but the recognizable cognate ‘genesis’. As in English, the Greek word ‘genesis’ has the basic meaning of ‘origin, source, or beginning’. We may recall the Greek name of the first book of the Bible was named ‘Genesis’ for this reason.
Translating the term as ‘birth’ or ‘generation’ here appears to be nothing more than trinitarian bias entering the translation process. Matthew knew the Greek words for ‘generation’ (gennao) and ‘birth’ (tikto), and uses both in the next few verses as he describes the virgin conception and birth of Jesus- but in verse 18, he chose a completely different word, one that is universally recognized as having the basic meaning of ‘origin’. This is crucial- Matthew is not presenting the following narrative of Jesus’s conception by the Holy Spirit and virgin birth as an account of the incarnation of a pre-existing spiritual being, as Trinitarians and Arians wish to affirm, but rather presents this account as the origin story of Jesus. This is precisely the christology of Biblical Unitarianism.
Now, we must not glance over the significance of this statement by Matthew here at the beginning of the New Testament. One may argue that something can literally pre-exist is birth, or its generation, but it is axiomatic that nothing literally pre-exists its own origin. And here we are told that the origin of Jesus Christ is his conception in the virgin Mary by the Holy Spirit, and subsequent virgin birth. That means that the person of Jesus Christ did not literally pre-exist his conception in Mary by the Holy Spirit. The Bible is telling us this in about as clear of terms as one could hope for, short of an explicit denial of literal pre-existence.
It is finally noteworthy here that Matthew does not tell us the origin (genesis) of a nature, a mere body, or a phase of Jesus’s life. Note well that according to Matthew, this is the account of the origin of Jesus Christ. Jesus Christ is a person, not a nature, or a body, or any other such thing; it is the very person of Jesus Christ that is in view here, and Matthew tells us the origin of this person is his conception in Mary by the Holy Spirit and subsequent virgin birth.
Interestingly, the apostle Paul seems familiar with this fact as well, and corroborates what Matthew says in Galatians 4:4;
But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law,Galatians 4:4, KJV
We may note that the King James Version here is much more faithful to the Greek than most modern translations, which instead read that God’s Son was “born of a woman”. Indeed, no one denies that Jesus was born of a woman, but this is not precisely what Paul has stated here; the Greek word he employs is the word ‘ginomai’, which is literally ‘to become’. It is frequently used of things coming into existence or being created in the New Testament, as in John 1:3, where it is translated ‘made’ in the phrase “all things were made by him, and without him nothing was made that has been made’. Modern translations like the NASB, attempting to more fully bring out the meaning of such passages, translate the word here as ‘come into being’, saying “All things came into being through Him, and apart from Him nothing came into being that has come into being.” Such translations reveal the opinion of translators as to actual meaning of the word ‘ginomai’ Paul employs here. Of its many hundreds of uses in the NT, modern translations almost never render the word ‘born’- with the notable exception of this passage. In the King James, the term was, in over 600 instances of the word, never once translated ‘born’.
So, what is the significance of Paul’s usage of the term here? Paul is, like Matthew, telling us Jesus’s origin. He uses a word here that means coming into being, telling us that God’s Son came into being from a woman. This dovetails nicely with what Matthew says Jesus’s origin is, that Jesus was conceived in a virgin woman by the Holy Spirit, and born of a virgin. The origin of Jesus for Paul, like Matthew, is Jesus coming forth from a woman.
While Matthew and Paul seem to straightforwardly tell us that Jesus took his origin from Mary by the Holy Spirit, its noteworthy that the language used by both these apostles is inconsistent with the view that the Son of God literally pre-existed. Matthew and Paul knew the Greek words for generation and birth, and could easily have used these words, and not wording communicating origination and coming into being, had they wished to communicate an incarnation rather than an origin. These statements of Matthew and Paul are not things that someone who believes the Son literally pre-existed, or who wants their reader to believe in his literal pre-existence, would say.
Finally, while we have generally addressed the time and manner of Christ’s origination from God, as being his generation in the virgin Mary through the agency of the Holy Spirit, and his subsequent virgin birth, we have yet to address that the Bible expressly says that this is indeed the generation (or begetting) on account of which Jesus is called the Son of God. Luke tells us:
And behold, you will conceive in your womb and bear a son, and you shall name Him Jesus. He will be great and will be called the Son of the Most High; and the Lord God will give Him the throne of His father David; and He will reign over the house of Jacob forever, and His kingdom will have no end.” Mary said to the angel, “How can this be, since I am a virgin?” The angel answered and said to her, “The Holy Spirit will come upon you, and the power of the Most High will overshadow you; and for that reason the holy Child shall be called the Son of God.Luke 1:31-35 NASB
Here we have it stated explicitly that the reason Jesus is called the Son of God is because of his having been begotten by God Most High in the womb of the virgin Mary, by the agency of the Holy Spirit. Jesus’s divine conception in Mary is the reason the Bible gives for him being called the Son of God- it is this begetting that makes Jesus “the only-begotten Son” of God. This runs totally contrary to Trinitarian and Arian christology, as for these viewpoints, the significance of Jesus being the Son of God is something going back long before he was conceived in the virgin Mary- either to his unique creation before the foundation of the world, or to an eternal generation. Either way, the reason that Jesus is the Son of God in these systems is something totally different than the reason the Bible gives.
To circle around to where we began, then, we can see from the Bible that Jesus is indeed caused by his Father, has his life from God, is begotten by God, and for this reason is God’s only-begotten Son. In this, historic Trinitarianism and Unitarianism agree. However, we went on to note that the explanation the Bible gives of these things is exactly the same as that given by Biblical Unitarians, and is exactly contrary to that given by Arians and Trinitarians. Jesus’s origin from the Father by being begotten by God is placed solely in time, not eternity, and identified clearly as Jesus’s miraculous conception in the virgin Mary and subsequent virgin birth; and we are told that it is on account of this miraculous generation from God that Jesus Christ is called God’s Son.