Hebrews 7:17

For he testifieth - That is, either the Scripture, in the place so often quoted, or God by that Scripture.

Thou art a priest for ever - This is the proof that he was not appointed according to the carnal commandment, but according to the power of an endless life, because he is a priest for ever; i.e. one that never dies, and is never disabled from performing the important functions of his office; for if he be a priest for ever, he ever lives.