marked off [the] Son of God by inherent ability according to [the] Spirit of holiness out from the resurrection from the dead, Jesus Christ our Lord (Romans 1:4).
Paul was separated unto God’s gospel concerning the One who would come from the seed of David. This one was marked as the Son of God. Sonship in Scripture does not relate to birth; it is a place of privilege (Galatians 4:1–2).
Jesus Christ, crucified by the hands of lawless men, was raised on the third day just as God stated, marking Him off as the Son (Acts 2:23–24). In Psalms 16:10, David records the promise of resurrection to Christ, “For you will not leave my soul in Sheol; You will not give your pious one to see corruption.”
And great is the confession of the mystery of godliness: God was manifested in flesh, justified by [the] Spirit, discerned by angels, proclaimed among the nations, believed on in the world, received into a proper opinion.”
Jesus Christ is God in the flesh. He is not a being created by God, but the second person of the Godhead incarnate. He was marked off as the Son by the Spirit of Holiness through the resurrection out from the dead, for no other man has ever been raised to die no more (Romans 6:9).