144 By assuming human nature, the Divine Word introduced into this earthly exile a hymn which is sung in heaven for all eternity. He unites to Himself the whole human race and with it sings this hymn to the praise of God. As we must humbly recognize that "we know not what we should pray for, as we ought, the Spirit Himself asketh for us with unspeakable groanings." Moreover, through His Spirit in us, Christ entreats the Father, "God could not give a greater gift to men . . . [Jesus] prays for us, as our Priest; He prays in us as our Head; we pray to Him as our God . . . we recognize in Him our voice and His voice in us . . . He is prayed to as God, He prays under the appearance of a servant; in heaven He is Creator; here, created though not changed, He assumes a created nature which is to be changed and makes us with Him one complete man, head and body."
Source: Mediator Dei (Vatican.va)