In its raw sense, "son of God" would normally mean a Godly person who is a devoted follower of God, dedicated to Godly service. We see this phrase, in plural form, used a number of times of ordinary humans who are Christians such as: Matt 5:9, Luke 20:30, Rom 8:14, 19, 9:26, Gal 3:26, 4:6. More often, this phrase is seen in a close variant, namely "children of God", 1 John 3:10, 5:2, Rom 9:8, Phil 2:15, etc.
However, there is a big difference between "sons of God", and, "The Son of God", namely Jesus Christ. I note that in Matt 26:63, the article is not (and cannot be) anaphoric, but must be monadic.
Now, no other person is referred to as "The Son of God"; even in Luke 3:38, speaking about Adam, the Greek phrase is τοῦ Θεοῦ = "of God" (implying the son of God; but more on this shortly.)
Now, even if we allow Adam as the original son of God and the father of humanity, the teaching of Rom 5:12-21 says (inter alia)
- Adam lost that title due to sin
- Jesus, as the second Adam, became the Father (Isa 9:6) of the saved, and thus, "The Son of God".
This can be confirmed by examining Jesus' reply to the High Priest - let me quote Matt 26:63-65 -
Then the high priest said to Him, “I charge You under oath by the
living God: Tell us if You are the Christ, the Son of God.”
“You have said it yourself,” Jesus answered. “But I say to all of you,
from now on you will see the Son of Man sitting at the right hand of
Power and coming on the clouds of heaven.”
At this, the high priest tore his clothes and declared, “He has
blasphemed! Why do we need any more witnesses? Look, now you have
heard the blasphemy.
From this exchange, we may conclude the following:
- Jesus had both titles, "The Son of God" (see Ps 2), and, "The Son of Man" (see Dan 7:13).
- That Jesus, with these titles was also Messiah
- that the High priest regarded these titles as a claim to divinity and thus accused Jesus of blasphemy
- As if to confirm this, Jesus, in the parallel passage in Mark 14:61-64, also used the expression, "I Am" (See Ex 3:13, 14)
- That Jesus was also the legitimate king of Israel, both literal and spiritual
Note that claiming to be a human messiah was nothing new. However, explicitly claiming to be both human (the Son of Man) and divine (the Son of God) and Messiah all at once, was (to them) quite blasphemous; but only if it was not true! This was confirmed by the High Priest illegally tearing his robes as a symbol of his disgust and horror of blasphemy.
Lastly, "The Son of God", as best I can determine, does not occur in the OT, except in Dan 3:25, clearly referring to a divine being. Adam is never referred to as "Son of God".
Thus, when the High Priest used the phrase, "The Son of God", he was either alluding to Dan 3:25, or, Jesus' followers' use of the title for Jesus at the time, which had become well-known and one of the sources of anger by Jewish leadership against Jesus. Indeed, it was this exchange (Matt 26:63-65) that sealed Jesus' condemnation and caused Him to be sentenced to death.
APPENDIX - Theology
Given that the High Priest was a Sadducee, whose beliefs excluded an after-life, it is extremely unlikely that the High Priest would have used the title, "The Son of God" to ask if Jesus was Adam. This is simply because Adam was long dead and could not (in the High Priest's thinking) be alive in Jesus.
