Yes, yes, a perpetual question of mine. I was doing research on Melchizedek again (b/c of my next Dews From Heaven post), and I remembered that the JST had some interesting details.
The JST for Hebrews 7 has these two verses about Melchizedek:
3 For this Melchizedek was ordained a priest after the order of the Son of God, which order was without father, without mother, without descent, having neither beginning of days, nor end of life. And all those who are ordained unto this priesthood are made like unto the Son of God, abiding a priest continually.
21 (For those priests were made without an oath; but this with an oath by him that said unto him, The Lord sware and will not repent, Thou art a priest forever after the order of Melchizedek;)
Does the “oath” or covenant have to do with the fact that this is forever? Is that the oath? That is will last, that the priest has become part of an order that never ends? It’s a good hypothesis, that of course needs much more time and attention. But I’ll try and keep that one in mind next time I work on D&C 84!