NOTES for Heb 5:10
In calling Christ "a priest forever according to the order of Melchizedek," the author of the letter turns to one of the most mysterious biblical figures. Melchizedek is indeed called in Genesis by a word traditionally translated as "priest," although in his time there could, of course, be no question yet of the Levitical priesthood.
The God whom Melchizedek serves is called by the name El Elyon, which appears nowhere else except in the story of Melchizedek's blessing of Abraham; Abraham's God was never called by this name. And this mysterious servant of an unknown god blesses Abraham, whom his God is leading. He blesses by revelation, by inspiration, not belonging to the people of God, appearing as if outside the history of Revelation and at the same time entering it in a completely unexpected way, beyond all frameworks and human ideas of salvation.
In the same way Christ Himself enters the world and the history of salvation: beyond every human framework, unexpectedly, unpredictably, violating and destroying all the messianic ideas and concepts of His era. But there is something else shared by Him and Melchizedek. As in every case when we are speaking of a phenomenon we today usually call charismatic, in the case of Melchizedek's blessing human nature played no very large role in this act.
Such spontaneous actions of a prophetic character are often performed, so to speak, "over" human nature. Of course, this is not what we see in Christ, in whom nature was fully and completely involved in each of His actions. But for fallen man, a charismatic act often turns out to be the only way to minimize the distortions that human sinfulness introduces into spiritual life. Every priest, for example, as one who presides, had first of all to resist his own sinfulness; otherwise, as a presider he could do nothing.
Jesus is simply free from sin; He does not need to struggle with Himself in order to carry out the ministry entrusted to Him by the Father. In this respect the charismatic Melchizedek is closer to Christ than an ordinary priest: he is, of course, not sinless, but in blessing Abraham he in a sense steps over his sinfulness with God's help. Of course, for Melchizedek this is only a brief state, while for Jesus it is normal; He was born this way and lives this way. But at the moment when Melchizedek understands that he must bless Abraham, he is closer to Christ than any priest overcoming his sinfulness in daily service. The sinless High Priest, who for the sake of people shared with them the lot of sinful man - this is how the Savior appears in the letter.