The first is that divine act of the Blessed Trinity by which the Second Person, the Eternal Son of the Father, assumed a created nature into the unity of His Person, and that the nature of man. The act whereby He became man is the act constituting His Priesthood.[83] Before His Incarnation He was not a Priest; in the divine nature in which alone He is from eternity, He does not offer but receive sacrifice. St. Paul describes the act, and the instantaneous acceptance by the Divine Son, as man in His human nature, of the mission to be High Priest for the human race in these words: "When He cometh into the world He saith: Sacrifice and oblation Thou wouldest not: but a body Thou hast fitted to me: Holocausts for sin did not please Thee. Then said I, behold I come: in the head of the book it is written of Me, that I should do Thy will, O God." The whole purpose of His Incarnation and the whole course of His future human life are here summed up, as accepted by Him in the first moment of His human existence, when He says: "A body Thou hast fitted to Me—behold I come—that I should do Thy will, O God." The whole Christian faith rests upon this divine act. It is the simply inconceivable humiliation of the Divine Majesty, the simply unutterable effect of the Divine Love. The angels, who have had it before them from their creation in vision, and for more than eighteen hundred years in effect, have not yet mastered its depths; nor is the Mother of fair Love herself—the nearest to it—equal to the task either of expressing it or of comprehending it. How, then, was it to be impressed on the human race in a manner which should cause its full force to be received by those who learnt it for the first time; and when it had been thus learnt what further provision was to bring about that it should never be forgotten, nor pass into the crowd of things which have once been and then cease to be? We have, first, in these words of St. Paul, the Divine Son accepting His mission as the first act of His human nature, and, further, expressing the nature of His mission—to do the will of His Father, that will being that He should take the body which His Father had prepared for Him. In that acceptance is comprised all the labours and sufferings of the thirty-three years foreseen from the beginning, willed by the Father, freely chosen by the Son in His manhood, as the first act of that manhood, which yet is prolonged through His whole life.