God has received us, once for all, into his family, to hold us not only as servants but as sons.  Thereafter, to fulfill the duties of a most excellent Father concerned for his offspring he undertakes also to nourish us throughout the course of our life.  And not content with this alone, he has willed, by giving his pledge, to assure us of this continuing liberality.  To this end, therefore, he has, through the hand of his only-begotten Son, given to his church another sacrament, that is, a spiritual banquet wherein Christ attests himself to be the life-giving bread, upon which our souls feed unto true and blessed immortality…the signs are bread and wine, which represent for us the invisible food we receive from the flesh and blood of Christ… Now Christ is the only food of our soul, and therefore our Heavenly Father invites us to Christ, that, refreshed by partaking of him, we may repeatedly gather strength until we shall have reached heavenly immortality.

Then Jesus said to them: “Most assuredly, I say to you, Moses did not give you the bread from heaven, but My Father gives you the true bread from heaven. 33For the bread of God is He who comes down from heaven and gives life to the world.” 34Then they said to Him, “Lord, give us this bread always.” 35And Jesus said to them, “I am the bread of life.  He who comes to Me shall never hunger, and he who believes in Me shall never thirst”…. “I am the living bread which came down from heaven. If anyone eats of this bread, he will live forever; and the bread that I shall give is My flesh, which I shall give for the life of the world” (John 6:32-35, 51).

Calvin on the Lord’s Supper, Institutes, vol. 3, XVII, Sec. 1