St. Paul opens his Epistle to the Romans by stating that the Lord Jesus Christ was “declared to be the Son of God with power,” or “powerfully declared to be the Son of God… by the resurrection from the dead” (1:4).
In Psa. 2:7, we have Christ, in prophecy, saying:
“I will declare the decree: the Lord hath said unto Me, Thou art My Son; this day have I begotten Thee.”
Our Lord was, of course, eternally one with the Father, but the word “begotten” here comes from Israel’s laws, referring to the time when the child was officially declared to be the father’s full-grown son.
But what day was He referring to? On what day did the Father officially proclaim:
“This day have I begotten Thee”?
The answer is found in Acts 13:33, where the Apostle states that God “raised up Jesus again; as it is also written in the second Psalm: Thou art My Son, this day have I begotten Thee.”
So our Lord was officially — and powerfully — declared to be the Son of God at His resurrection from the dead. But what did Paul mean in II Tim. 2:7,8, where he said:
“Consider what I say; and the Lord give thee understanding in all things. Remember that Jesus Christ, of the seed of David, was raised from the dead ACCORDING TO MY GOSPEL.”
The answer is that the twelve had proclaimed Christ as the Son of David, to sit on David’s throne. Theirs was “the gospel of the kingdom.” But when the King and His kingdom were rejected, God raised up another apostle, Paul, to proclaim “the gospel of the grace of God” (Acts 20:24).
Christ was, indeed, raised from the dead to sit on David’s throne, and this will yet come to pass, but Paul has a message for us, here and now: that Christ was raised from the dead to certify our justification and to become the Head of “the Church which is His Body.” source