Hebrews 7:3, 8, 23-25

Without [any record of] father or mother, nor ancestral line, without [any record of] beginning of days (birth) nor ending of life (death), but having been made like the Son of God, he remains a priest without interruption and without successor.

Furthermore, here [in the Levitical priesthood] tithes are received by men who are subject to death; but in that case [concerning Melchizedek], they are received by one of whom it is testified that he lives on [perpetually].

The [former successive line of] priests, on the one hand, existed in greater numbers because they were each prevented by death from continuing [perpetually in office]; but, on the other hand, Jesus holds His priesthood permanently and without change, because He lives on forever. Therefore He is able also to save forever (completely, perfectly, for eternity) those who come to God through Him, since He always lives to intercede and intervene on their behalf [with God].