[These are the words of St. Paul describing the Christian priesthood, modeled upon Christ as the High Priest.]
For every high priest taken from among men is appointed for men in the things pertaining to God, that he may offer gifts and sacrifices for sins.
He is able to have compassion on the ignorant and erring, because he himself also is beset with weakness, and by reason thereof is obliged to offer for sins, as on behalf of the people, so also for himself.
And no man takes the honor to himself; he takes it who is called by God, as Aaron was.
So also Christ did not glorify himself with the high priesthood, but he who spoke to him, Thou art my son, I this day have begotten thee.
As he says in another place, Thou art a priest forever, according to the order of Melchisedech.
For Jesus, in the days of his earthly life, with a loud cry and tears, offered up prayers and supplications to him who was able to save him from death, and was heard because of his reverent submission.
And he, Son though he was, learned obedience from the things that he suffered; and when perfected, he became to all who obey him the cause of eternal salvation, called by God a high priest according to the order of Melchisedech.
[When St. Paul says that Jesus became "perfected," he does not mean that Jesus was not already perfect. St. Paul means that after Jesus resurrected from the dead he was perfected in wearing his glorified heavenly body, even as he stayed on earth in that glorified body for forty days before ascending to heaven. Remember that St. Paul never met Jesus of the earthly body, but met the resurrected Jesus in the glory of heaven on the road to Damascus.
Likewise, when St. Paul says Jesus "learned" obedience, it is not like Jesus wasn't already in perfect obedience from boyhood. In the Bible "learned" often means the same as "practiced." Thus St. Paul is explaining that Jesus practiced and thus provided the role model of perfect obedience even when there is great suffering, if it is God's will. You have to use common sense when reading the Bible. For example they use the word "knew" his wife to indicate having intimacy to bear a child; it's not like the husband and wife didn't "know" each other until that moment. Likewise perfected and learning are words that describe repetitions and progressive actions, not indicating the lack of those qualities "previously."]