Hebrews 7:17 - Matthew Poole's English Annotations on the Holy Bible

For he testifieth: this is proved by infallible testimony in Psalms 110:4, God the Father himself solemnly declared him to be so before the angels in heaven, and revealed it to men on earth by the prophet David. Thou art a Priest for ever after the order of Melchisedec: that as Melchisedec had no end of days recorded, so this is repeated again to prove, that the Priest after his similitude, i.e. after his order, (the words being here synonymous), must continue for ever. Christ was not a temporary Priest by a carnal law, but was made a Priest for ever, with everlasting power endowed to save all his people: see Hebrews 7:24,25,28, and Matthew 1:21.