Hebrews 5:6

6. After the order of Melchizedek Christ was no descendant of Aaron, and so could be no high priest in the hereditary Jewish line. High priest he can be only by an origination high, at least, as Aaron’s own origination at first was. For this the inspired precedent is found in the most memorable words of Psalms 110:4, (a psalm quoted as Messianic by the Messiah himself, Matthew 22:44,) where the Messiah is addressed by God as priest, not in the line of Aaron, but after the order of Melchizedek. And here first occurs the name of that primeval and typical priest-king, which figures largely in our author’s future argument.