4 To know with an entire faith what is the excellence of the Most Holy Eucharist is in truth to know what that work is which, in the might of His mercy, God, made man, carried out on behalf of the human race. For as a right faith teaches us to acknowledge and to worship Christ as the sovereign cause of our salvation, since He by His wisdom, His laws, His ordinances, His example, and by the shedding of His blood, made all things new; so the same faith likewise teaches us to acknowledge Him and to worship Him as really present in the Eucharist, as verily abiding through all time in the midst of men, in order that as their Master, their Good Shepherd, their most acceptable Advocate with the Father, He may impart to them of His own inexhaustible abundance the benefits of that redemption which He has accomplished. Now if any one will seriously consider the benefits which flow from the Eucharist he will understand that conspicuous and chief among them all is that in which the rest, without exception, are included; in a word it is for men the source of life, of that life which best deserves the name. "The bread which I will give is my flesh, for the life of the world" (St. John vi., 52). In more than one way, as We have elsewhere declared, is Christ "the life." He Himself declared that the reason of His advent among men was this, that He might bring them the assured fulness of a more than merely human life. "I am come that they may have life, and may have it more abundantly" (St. John x., 10). Everyone is aware that no sooner had "the goodness and kindness of God our Saviour appeared" (Tit. iii., 4), than there at once burst forth a certain creative force which issued in a new order of things and pused through all the veins of society, civil and domestic. Hence arose new relations between man and man; new rights and new duties, public and private; henceforth a new direction was given to government, to education, to the arts; and most important of all, man's thoughts and energies were turned towards religious truth and the pursuit of holiness. Thus was life communicated to man, a life truly heavenly and divine. And thus we are to account for those expressions which so often occur in Holy Writ, "the tree of life," "the word of life," "the book of life," "the crown of life," and particularly "the bread of life."
Source: Mirae Caritatis (Vatican.va)