In bringing many sons to glory, it was befitting that He for whom and by whom the universe exists, should perfect the Pioneer of their salvation by suffering.
Previous priests became priests apart from any oath, but he has an oath from Him who said to him, The Lord has sworn, and he will not change his mind, thou art a priest for ever.
He has neither father nor mother nor genealogy, neither a beginning to his days nor an end of his life, but, resembling the Son of God, continues to be priest permanently.
Similarly Christ was not raised to the glory of the high priesthood by himself but by Him who declared to him, Thou art my son, to-day have I become thy father.
He had to resemble his brothers in every respect, in order to prove a merciful and faithful high priest in things divine, to expiate the sins of the People.