God hath fulfilled the same unto us their children, in that he {o} hath raised up Jesus again; {13} as it is also written in the second psalm, Thou art my Son, this day have I begotten thee.

(o) For then he appeared plainly and manifestly as the only Son of God, when he left behind his weakness and came out of the grave, having conquered death.

(13) If Christ had remained dead, he would not have been the true Son of God, neither would the covenant which was made with David have been certain.

People's New Testament

13:33 Thou art my Son, this day have I begotten thee. See Ps 2:7. Paul gives the thought in Ro 1:4: He was declared to be the Son of God with power, by the resurrection from the dead.

Wesley's Notes

13:33 Thou art my Son, this day have I begotten thee - It is true, he was the Son of God from eternity. The meaning therefore is, I have this day declared thee to be my Son. As St. Paul elsewhere, declared to be the Son of God with power, by the resurrection from the dead, Rom 1:4. And it is with peculiar propriety and beauty that God is said to have begotten him, on the day when he raised him from the dead, as he seemed then to be born out of the earth anew. Psalm 2:7.

Jamieson-Fausset-Brown Bible Commentary

33. God hath fulfilled the same-"hath completely fulfilled."

in that he hath raised up Jesus again-literally, "raised up"; but the meaning is (notwithstanding the contrary opinion of many excellent interpreters) "from the dead"; as the context plainly shows.

as it is written in the second psalm-in many manuscripts "the first Psalm"; what we call the first being regarded by the ancient Jews as only an introduction to the Psalter, which was considered to begin with the second.

this day have I begotten thee-As the apostle in Ro 1:4 regards the resurrection of Christ merely as the manifestation of a prior Sonship, which he afterwards (Ac 8:32) represents as essential, it is plain that this is his meaning here. (Such declarative meaning of the verb "to be" is familiar to every reader of the Bible). See Joh 15:8, "So shall ye be," that is, be seen to be "My disciples." It is against the whole sense of the New Testament to ascribe the origin of Christ's Sonship to His resurrection.

Matthew Henry's Concise Commentary

13:32-37 The resurrection of Christ was the great proof of his being the Son of God. It was not possible he should be held by death, because he was the Son of God, and therefore had life in himself, which he could not lay down but with a design to take it again. The sure mercies of David are that everlasting life, of which the resurrection was a sure pledge; and the blessings of redemption in Christ are a certain earnest, even in this world. David was a great blessing to the age wherein he lived. We were not born for ourselves, but there are those living around us, to whom we must study to be serviceable. Yet here is the difference; Christ was to serve all generations. May we look to Him who is declared to be the Son of God by his resurrection from the dead, that by faith in him we may walk with God, and serve our generation according to his will; and when death comes, may we fall asleep in him, with a joyful hope of a blessed resurrection.