17 No sooner, in fact, "is the Word made flesh" than he shows Himself to the world vested with a priestly office, making to the Eternal Father an act of submission which will continue uninterruptedly as long as He lives: "When He cometh into the world he saith. . . 'behold I come . . . to do Thy Will." This act He was to consummate admirably in the bloody Sacrifice of the Cross: "It is in this will we are sanctified by the oblation of the Body of Jesus Christ once." He plans His active life among men with no other purpose in view. As a child He is presented to the Lord in the Temple. To the Temple He returns as a grown boy, and often afterwards to instruct the people and to pray. He fasts for forty days before beginning His public ministry. His counsel and example summon all to prayer, daily and at night as well. As Teacher of the truth He "enlighteneth every man" to the end that mortals may duly acknowledge the immortal God, "not withdrawing unto perdition, but faithful to the saving of the soul." As Shepherd He watches over His flock, leads it to life-giving pasture, lays down a law that none shall wander from His side, off the straight path He has pointed out, and that all shall lead holy lives imbued with His spirit and moved by His active aid. At the Last Supper He celebrates a new Pasch with solemn rite and ceremonial, and provides for its continuance through the divine institution of the Eucharist. On the morrow, lifted up between heaven and earth, He offers the saving sacrifice of His life, and pours forth, as it were, from His pierced Heart the sacraments destined to impart the treasures of redemption to the souls of men. All this He does with but a single aim: the glory of His Father and man's ever greater sanctification.
Source: Mediator Dei (Vatican.va)