Melchizedek was a priest of the Bible's God who lived in Abraham's day prior to the birth of Levi, Moses, and Aaron; and subsequently prior to the Aaronic priesthood (Gen 14:17-20). Aaron's priesthood-- along with its attendant retinue of under-priests --is THE priesthood for people whose religion consists of the commandments.
In contrast, Melchizedek's priesthood had no connection to the commandments whatsoever; therefore, his constituents (which included Abraham) were not required to obey the commandments because they didn't become law till a few hundred years later (Gal 3:17). So then it was, and still is, impossible for a Melchizedekian priest's constituents to break the commandments.
†.Rom 4:15 . .where no commandments exist; there is no transgression.
So then, what does this mean in practical terms?
The Bible's Jesus is clearly stated to be a priest like Melchizedek.
†.Heb 5:4-6 . .So also Christ did not glorify Himself so as to become a high priest, but He who said to him, "Thou art My Son, Today I have begotten Thee" and also "Thou art a priest forever according to the order of Melchizedek."
ergo: People trying to earn salvation points via the commandments are mixed up with the wrong priesthood because Melchizedek's order doesn't mediate for people whose religion consists of the commandments. Those people are inadvertently relying upon the now-obsolete Aaronic order rather than Melchizedek's; viz: Jesus is of no use to them whatsoever; and they are in grave danger of the wrath of God.
†.Gal 3:10 . .For as many as are of the works of the commandments are under a curse; for it is written, "Cursed is everyone who does not continually abide by all things written in the book of the law, to perform them." (Deut 27:26)
†.Heb 7:11 . .Now if perfection was through the Aaronic priesthood (for on the basis of it the people received the commandments), what further need was there for another priest to arise according to the order of Melchizedek, and not be designated according to the order of Aaron?
The answer to that question is quite simple. No flesh will be adjudged innocent in God's court by keeping the commandments simply because no flesh can obey them consistently (Rom 3:19-20). Therefore, Melchizedek's priesthood is mankind's only hope of escape from retribution.
†.Heb 5:8-10 . .He became, to all those who heed him, the source of eternal salvation, being designated by God as a High Priest according to the order of Melchizedek.
†.Heb 6:19-20 . .This hope we have as an anchor of the soul, a hope both sure and steadfast and one which enters within the veil, where Jesus has entered as a forerunner for us, having become a High Priest forever according to the order of Melchizedek.
Religions that require their adherents to comply with the commandments in order to be worthy to escape eternal suffering, rather than depending entirely upon Jesus' priesthood; are religions that doom their members to a status that the Bible calls: fallen from grace and alienated from Christ.
†.Gal 5:3-5 . .For if you are trying to make yourselves righteous with God by keeping the commandments, then you have been severed from Christ! You have fallen from grace.
†.Gal 2:21 . .I am not one of those who treats the kindness of God as meaningless. For if we could be spared by keeping the commandments, then there was no need for Christ to die.
†.Gal 3:21-22 . .If the commandments could have given us new life, then we could have been made right with God by obeying them. But the Scriptures have declared that we are all prisoners of sin, so the only way to receive God's promise is to rely upon Jesus Christ.
†.Rom 6:23 . .For the wages of sin is death; but the gift of God is eternal life in Messiah Jesus