(For those priests were made without an oath; but this with an oath by him that said unto him,
The Lord swore and will not change, you are a priest forever after the order of Melchizedek:
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Hippolytus of Rome
For also our Father, on beholding the Good One, and on being initiated with Him, preserved the mysteries respecting which silence is enjoined, and sware, as it has been written, "The Lord sware, and will not repent.".
And this oath, (Justinus) says, our Father Elohim sware when He was beside the Good One, and having sworn He did not repent (of the oath), respecting which, he says, it has been written, "The Lord sware, and will not repent." ...
And inasmuch as not without an oath. What is And inasmuch as not without an oath? That is, Behold another difference also. And these things were not merely promised (he says). For those priests were made without an oath, Hebrews 7:21-22 but This with an oath, by Him that said unto Him, The Lord swore and will not repent, You are Priest for ever after the order of Melchisedec. By so much was Jesus made a surety of a better covenant. He lays down two points of difference, that it has no end as the [covenant] of the Law had; and this he proves from [its being] Christ who exercises [the priesthood]; for he says according to the power of an endless life. And he proves it also from the oath, because He swore, etc., and from the fact; for if the other was cast out, because it was weak, this stands firm, because it is powerful. He proves it also from the priest. How? Because He is One [only]; and there would not have been One [only], unless He had been immortal. For as there were many priests,...