For unto which of the angels said he at any time, Thou art my Son, this day have I begotten thee? And again, I will be to him a Father, and he shall be to me a Son? And again, when he bringeth in the first begotten into the world, he saith, And let all the angels of God worship him. And of the angels he saith, Who maketh his angels spirits, and his ministers a flame of fire. But unto the Son he saith, Thy throne, O God, is for ever and ever: a sceptre of righteousness is the sceptre of thy kingdom. ~ Hebrews 1:5-8

In Acts 13, the apostle Paul interprets the same text quoted by the writer of Hebrews from Psalm 2, as referring to the resurrection of Jesus.

God hath fulfilled the same unto us their children, in that he hath raised up Jesus again; as it is also written in the second psalm, Thou art my Son, this day have I begotten thee. And as concerning that he raised him up from the dead, now no more to return to corruption, he said on this wise, I will give you the sure mercies of David. Wherefore he saith also in another psalm, Thou shalt not suffer thine Holy One to see corruption. ~ Acts 13:33-35

Paul interprets the words Thou art my Son, this day have I begotten thee (Psalm 2:7), as a reference to the resurrection of Jesus and not the incarnation. Therefore, we can be confident that the writer of Hebrews has the resurrection in mind when he quotes it in his epistle.

In chapter 1 he cites Psalms 2:7 to show us the superiority of Jesus to the angels. In chapter 5 he cites it again to show us the superiority of Christ at High Priest to the priesthood of Aaron. 

So also Christ glorified not himself to be made an high priest; but he that said unto him, Thou art my Son, to day have I begotten thee. As he saith also in another place, Thou art a priest for ever after the order of Melchisedec. ~ Hebrews 5:5-6

Now, consider Paul’s words from Romans 1 which ties these two truths together.

Paul, a servant of Jesus Christ, called to be an apostle, separated unto the gospel of God, (Which he had promised afore by his prophets in the holy scriptures,) Concerning his Son Jesus Christ our Lord, which was made of the seed of David according to the flesh; And declared to be the Son of God with power, according to the spirit of holiness, by the resurrection from the dead … ~ Romans 1:1-4

God’s Son was made of the seed of David. The writer of Hebrews says he did not take on the nature of angels but he took on the seed of Abraham (2:16). Jesus, the Son of God, is the Son of Man (the Man who came down from above) to die and rise again on behalf of all the sons of men, to deliver us from the power of darkness and to bring us near to God. 

Being the firstborn from the dead does not mean that Jesus is a born again man as some erroneously teach. It means that in his flesh, i.e., in his humanity, he triumphed over sin and death through his resurrection and has become our Great High Priest representing us in the sight of a Holy God. In Jesus, God and man meet and thus we have redemption, reconciliation, and the remission of our sins in him.

In his incarnation he is the only begotten of the Father, in his resurrection he has become the firstborn among many brethren. He is both God with us and the one who brings us to God. He is God in our midst, and the one who leads us in praise to God! Hallelujah!

But we see Jesus, who was made a little lower than the angels for the suffering of death, crowned with glory and honour; that he by the grace of God should taste death for every man. For it became him, for whom are all things, and by whom are all things, in bringing many sons unto glory, to make the captain of their salvation perfect through sufferings. For both he that sanctifieth and they who are sanctified are all of one: for which cause he is not ashamed to call them brethren, Saying, I will declare thy name unto my brethren, in the midst of the church will I sing praise unto thee. And again, I will put my trust in him. And again, Behold I and the children which God hath given me. Forasmuch then as the children are partakers of flesh and blood, he also himself likewise took part of the same; that through death he might destroy him that had the power of death, that is, the devil; And deliver them who through fear of death were all their lifetime subject to bondage. For verily he took not on him the nature of angels; but he took on him the seed of Abraham. Wherefore in all things it behoved him to be made like unto his brethren, that he might be a merciful and faithful high priest in things pertaining to God, to make reconciliation for the sins of the people. For in that he himself hath suffered being tempted, he is able to succour them that are tempted. ~ Hebrews 2:9-18