Romans 1:3-4, Jesus Becomes God's Son

[C]oncerning His Son Jesus Christ our Lord, who was born of the seed of David according to the flesh, and declared to be the Son of God with power according to the Spirit of holiness, by the resurrection from the dead.  

//Here's a question that intrigued early Christians. At what point did Jesus become God's son?

We all know the birth stories in Matthew and Luke, and their claim that God impregnated Mary and conceived a son. Surely that is the moment Jesus became the Son of God?

Another, probably earlier, tradition comes from the book of John. John mentions nothing at all about a virgin birth, and instead tells how Jesus was anointed as the Son of God at his baptism. (Technically, John doesn't mention the baptism itself, but we may infer the event.) So could this be the day? Many early Christians accepted this "adoptionist" explanation and saw nothing heretical in it.

An even earlier tradition is found in Paul's letter to the Romans. In today's verse, Paul cites a probable creed that Jesus was born of the flesh (of the lineage of King David) and became the Son of God only after the resurrection! Surprisingly, the book of Acts, which was authored by the same person as the Gospel of Luke and its virgin birth story, appears to side with Paul! 

"God has fulfilled this for us their children, in that He has raised up Jesus. As it is also written in the second Psalm: 'You are My Son, Today I have begotten You.' And that He raised Him from the dead ..." - Acts 13:32-33

Scholars generally consider this passage in Acts to be a primitive tradition that long predated the day it was copied by Luke. Most likely, the understanding was that Jesus rose from the dead and immediately ascended to heaven, having been adopted by God. So we have several traditions that show a bit of a progression:

[1] The earliest: Jesus became God's son when resurrected.

[2] A bit later: Jesus became God's son when anointed by the Spirit at his baptism.

[3] Later still: Jesus is the literal offspring of God and a human woman, and became God's son at conception.

[4] As doctrines merged, church fathers began to entangle the incarnating (anointing) Spirit with its human host, and decided Jesus had been the Son of God since before time.