This is an extended quote pulled form Calvin’s Institutes of the Christian Religion. Commonly referred to as The Institutes, it was first published in 1536. The translation below was done by Henry Beveridge.
First, then, the signs are bread and wine, which represent the invisible food which we receive from the body and blood of Christ. For as God, regenerating us in baptism, ingrafts us into the fellowship of his Church, and makes us his by adoption, so we have said that he performs the office of a provident parent, in continually supplying the food by which he may sustain and preserve us in the life to which he has begotten us by his word. Moreover, Christ is the only food of our soul, and, therefore, our heavenly Father invites us to him, that, refreshed by communion with him, we may ever and anon gather new vigour until we reach the heavenly immortality. But as this mystery of the secret union of Christ with believers is incomprehensible by nature, he exhibits its figure and image in visible signs adapted to our capacity, nay, by giving, as it were, earnests and badges, he makes it as certain to us as if it were seen by the eye; the familiarity of the similitude giving it access to minds however dull, and showing that souls are fed by Christ just as the corporeal life is sustained by bread and wine. We now, therefore, understand the end which this mystical benediction has in view—viz. to assure us that the body of Christ was once sacrificed for us, so that we may now eat it, and, eating, feel within ourselves the efficacy of that one sacrifice,—that his blood was once shed for us so as to be our perpetual drink. This is the force of the promise which is added, “Take, eat; this is my body, which is broken for you” (Mt. 26:26, &c.).
If you would like to read more, go to https://www.ccel.org/ccel/calvin/institutes
If you would like to read more about John Calvin, here is a start http://www.christianitytoday.com/history/people/theologians/john-calvin.html