John 17:19

19. Sanctify myself The great conditional sanctification or consecration of himself, by which Christ entitled himself to redeem a glorious Church from out the world, and present it pure and perfect before the Father, was the suffering of death. Thus as a redeemer he was made perfect through suffering.

For their sakes This consecrating agony was undergone for the sake of his apostles, constituting and representing his entire glorious Church.