Hebrews 5:5

So also Christ glorified not himself to be made an
high priest
It was a glorifying of Christ, to make him an high priest; not as God, for as such no addition can be made to his glory; yea, it was a condescension in him to become a priest: but as man; it was an honour to the human nature to be united to the Son of God; and to be separated from others to this office; and to be called unto it, qualified for it, and invested with it; and to be of the order he was, and to do the work; and the very assistance he had in it, for the accomplishment of it, was a glorifying of him, for which he prayed; and the work being done, he had glory given him by his Father; and an ascription of glory is made to him by angels and saints: but Christ did not take this high and honourable office to himself, nor the glory of it; indeed, he did not receive it from man, nor was he made a priest according to the ceremonial law; yet he did not intrude himself into this office:

but he that said unto him, thou art my Son, today have I
begotten thee;
he appointed him to this office; he sent him to execute it; he anointed him with the oil of gladness above his fellows; he consecrated and established him in it with an oath; and prescribed to him what he should do, suffer, and offer; and declared to him what he might expect as the reward thereof. These words are taken out of ( Psalms 2:7 ) , (See Gill on Hebrews 1:5), and they are not to be considered as constitutive of Christ's priesthood, as if that was intended by the begetting of him as a Son; but as descriptive of the person, who called him to it, who stood in the relation of a Father to Christ, and Christ in the relation of a Son to him; therefore the one was very proper to call, and the other a very fit person to be called to this office, being every way capable of executing it, to the glory of God, and to the good of men.