You Are My Son.

This scripture the apostle quotes (Hebrews 1:5) to prove that Christ has a more excellent name than the angels, but that he obtained it by inheritance, Psalm 2:4. He is the Son of God, not by adoption, but his begotten Son, the only begotten of the Father, John 1:14. And the Father owns him, and will have this declared to the world as the reason why he is constituted King upon the holy hill of Zion he is therefore unquestionably entitled to, and perfectly qualified for, that great trust. He is the Son of God, and therefore of the same nature with the Father, has in him all the fulness of the godhead, infinite wisdom, power, and holiness. The supreme government of the church is too high an honour and too hard an undertaking for any mere creature none can be fit for it but he who is one with the Father and was from eternity by him as one brought up with him, thoroughly apprized of all his counsels, Proverbs 8:30. He is the Son of God, and therefore dear to him, his beloved Son, in whom he is well pleased and upon this account we are to receive him as a King for because the Father loveth the Son he hath given all things into his hand, John 3:35,5:20. Being a Son, he is heir of all things, and, the Father having made the worlds by him, it is easy to infer thence that by him also he governs them for he is the eternal Wisdom and the eternal Word. If God hath said unto him, "Thou art my Son," it becomes each of us to say to him, "Thou art my Lord, my sovereign." Further, to satisfy us that his kingdom is well-grounded upon his sonship, we are here told what his sonship is grounded on: This day have I begotten thee, which refers both to his eternal generation itself, for it is quoted (Hebrews 1:5) to prove that he is the brightness of his Father's glory and the express image of his person (Psalm 2:3), and to the evidence and demonstration given of it by his resurrection from the dead, for to that also it is expressly applied by the apostle, Acts 13:33. He hath raised up Jesus again, as it is written, Thou art my Son, this day have I begotten thee. It was by the resurrection from the dead, that sign of the prophet Jonas, which was to be the most convincing of all, that he was declared to be the Son of God with power, Romans 1:4. Christ is said to be the first-begotten and first-born from the dead, Revelation 1:5; Colossians 1:18. Immediately after his resurrection he entered upon the administration of his mediatorial kingdom it was then that he said, All power is given unto me, and to that especially he had an eye when he taught his disciples to pray, Thy kingdom come. - Matthew Henry