And declared to be the Son of God with power, according to the spirit of holiness, by the resurrection from the dead: And declared to be the Son of God - See the note on Acts 13:33, where this subject is considered at large. The word ορισθεντος, which we render declared, comes from οριζω, to bound, define, determine, or limit, and hence our word horizon, the line that determines the farthest visible part of the earth, in reference to the heavens. In this place the word signifies such a manifest and complete exhibition of the subject as to render it indubitable. The resurrection of Christ from the dead was such a manifest proof of our Lord's innocence, the truth of his doctrine, and the fulfillment of all that the prophets had spoken, as to leave no doubt on any considerate and candid mind.
With power - εν δυναμει, With a miraculous display of Divine energy; for, how could his body be raised again, but by the miraculous energy of God? Some apply the word here to the proof of Christ's sonship; as if it were said that he was most manifestly declared to be the Son of God, with such powerful evidence and argument as to render the truth irresistible.
According to the spirit of holiness - There are many differences of sentiment relative to the meaning of this phrase in this place; some supposing that the spirit of holiness implies the Divine nature of Jesus Christ; others, his immaculate sanctity, etc. To me it seems that the apostle simply means that the person called Jesus, lately crucified at Jerusalem, and in whose name salvation was preached to the world, was the Son of God, the very Messiah promised before in the holy Scriptures; and that he was this Messiah was amply demonstrated.
1st, By his resurrection from the dead, the irrefragable proof of his purity, innocence, and the Divine approbation; for, had he been a malefactor, as the Jews pretended, the miraculous power of God would not have been exerted in raising his body from the dead.
2nd, He was proved to be the Son of God, the promised Messiah, by the Holy Spirit, (called here the spirit of holiness), which he sent down upon his apostles, and not on them only, but on all that believed on his name; by whose influence multitudes were convinced of sin, righteousness, and judgment, and multitudes sanctified unto God; and it was by the peculiar unction of this spirit of holiness, that the apostles gave witness of the resurrection of the Lord Jesus, Acts 4:33.
Thus, then, Christ was proved to be the true Messiah, the son of David according to the flesh, having the sole right to the throne of Israel; and God recognized this character, and this right, by his resurrection from the dead, and sending forth the various gifts and graces of the Spirit of holiness in his name.