I will declare the {d} decree: the LORD hath said unto me, Thou art my Son; this {e} day have I begotten thee.

(d) To show that my calling to the kingdom is from God.

(e) That is to say, concerning man's knowledge, because it was the first time that David appeared to be elected by God. So it is applied to Christ in his first coming and manifestation to the world.

Wesley's Notes

2:7 The decree - The will and appointment of God concerning this. My sin - Which tho' it may in some sort be said to, or of David, yet much more properly belongs to Christ, who is commonly known by this title both in the Old and New Testament, and to whom this title is expressly appropriated by the holy ghost, who is the best interpreter of his own words, Acts 13:33 Heb 1:5. This day - This may be understood either, Of his eternal generation. This day, from all eternity, which is well described by this day, because in eternity there is no succession, no [yesterday,] no [tomorrow,] but it is all as one continued day or moment without change or flux; or, Of the manifestation of Christ's eternal son - ship in time; which was done both in his birth and life, when his being the son of God was demonstrated by the testimony of the angel, Luke 1:32, and of God the Father, Matt 3:17 17:5, and by his own words and works; and in his resurrection, which seems to be here mainly intended, of which day this very place is expounded, Acts 13:33. When Christ was in a most solemn manner declared to be the son of God with power, Rom 1:4.

King James Translators' Notes

the decree: or, for a decree

Jamieson-Fausset-Brown Bible Commentary

7. The king thus constituted declares the fundamental law of His kingdom, in the avowal of His Sonship, a relation involving His universal dominion.

this day have I begotten thee-as 2Sa 7:14, "he shall be My son," is a solemn recognition of this relation. The interpretation of this passage to describe the inauguration of Christ as Mediatorial King, by no means impugns the Eternal Sonship of His divine nature. In Ac 13:33, Paul's quotation does not imply an application of this passage to the resurrection; for "raised up" in Ac 13:32 is used as in Ac 2:30; 3:22, &c., to denote bringing Him into being as a man; and not that of resurrection, which it has only when, as in Ac 2:34, allusion is made to His death (Ro 1:4). That passage says He was declared as to His divine nature to be the Son of God, by the resurrection, and only teaches that that event manifested a truth already existing. A similar recognition of His Sonship is introduced in Heb 5:5, by these ends, and by others in Mt 3:17; 17:5.

Matthew Henry's Concise Commentary

2:7-9 The kingdom of the Messiah is founded upon an eternal decree of God the Father. This our Lord Jesus often referred to, as what he governed himself by. God hath said unto him, Thou art my Son, and it becomes each of us to say to him, Thou art my Lord, my Sovereign'. The Son, in asking the heathen for his inheritance, desires their happiness in him; so that he pleads for them, ever lives to do so, and is able to save to the uttermost, and he shall have multitudes of willing, loyal subjects, among them. Christians are the possession of the Lord Jesus; they are to him for a name and a praise. God the Father gives them to him, when, by his Spirit and grace, he works upon them to submit to the Lord Jesus.