John Calvin, from his Institutes of Religion: 4.17.4-5
4. Therefore, it is not the principal part of a sacrament simply to hold forth the body of Christ to us without any higher consideration, but rather to seal and confirm that promise by which he testifies that his flesh is meat indeed, and his blood drink indeed, nourishing us unto life eternal, and by which he affirms that he is the bread of life, of which, whosoever shall eat, shall live for ever — I say, to seal and confirm that promise, and in order to do so, it sends us to the cross of Christ, where that promise was performed and fulfilled in all its parts. For we do not eat Christ duly and savingly unless as crucified, while with lively apprehension we perceive the efficacy of his death. When he called himself the bread of life, he did not take that appellation from the sacrament, as some perversely interpret; but such as he was given to us by the Father, such he exhibited himself when becoming partaker of our human mortality, he made us partakers of his divine immortality; when offering himself in sacrifice, he took our curse upon himself, that he might cover us with his blessing, when by his death he devoured and swallowed up death, when in his resurrection he raised our corruptible flesh, which he had put on, to glory and incorruption.
5. It only remains that the whole become ours by application. This is done by means of the gospel, and more clearly by the sacred Supper, where Christ offers himself to us with all his blessings, and we receive him in faith. The sacrament, therefore, does not make Christ become for the first time the bread of life; but, while it calls to remembrance that Christ was made the bread of life that we may constantly eat him, it gives us a taste and relish for that bread, and makes us feel its efficacy. For it assures us, first, that whatever Christ did or suffered was done to give us life; and, secondly, that this quickening is eternal; by it we are ceaselessly nourished, sustained, and preserved in life. For as Christ would not have not been the bread of life to us if he had not been born, if he had not died and risen again; so he could not now be the bread of life, were not the efficacy and fruit of his nativity, death, and resurrection, eternal. All this Christ has elegantly expressed in these words, "The bread that I will give is my flesh, which I will give for the life of the world" (John 6:51); doubtless intimating, that his body will be as bread in regard to the spiritual life of the soul, because it was to be delivered to death for our salvation, and that he extends it to us for food when he makes us partakers of it by faith. Wherefore he once gave himself that he might become bread, when he gave himself to he crucified for the redemption of the world; and he gives himself daily, when in the word of the gospel he offers himself to be partaken by us, inasmuch as he was crucified, when he seals that offer by the sacred mystery of the Supper, and when he accomplishes inwardly what he externally designates.