I am the living bread. He (Jesus) often repeats the same thing because nothing is more necessary to be known, and every one feels in himself with what difficulty we are brought to believe it and how easily and quickly it passes away and is forgotten. We all desire life, but in seeking it, we foolishly and improperly wander about in circuitous roads, and when it is offered, the greater part disdainlully reject it. For who is there athat does not contrive for himself life out of Christ?  And how few there are who satisfied with Christ alone!  It is not a superfluous repetition, therefore, when Christ asserts so frequently that he alone is sufficient to give life. For he claims for himself the designation of bread, in order to tear from our hearts all fallacious hopes of living.  Having formerly called himself the bread of life, he now calls himself the living bread, but in the same sense–namely, life-giving bread.

Which have come down from heaven. He frequently mentions his coming down from heaven, because spiritual and incorruptible life will not be found in this world, the fashion of which passes away and vanishes, but only in the heavenly kingdom of God.

If any man eat of this bread. Whenever he uses the word eat, he exorts us to faith, which alone enables us to enjoy this bread, so as to derive life from it. Nor is it without good reason that he does so, for there are few who deign to stretch out their hand to put this bread to their mouth; even when the Lord puts it into their mouth, there are but few who relish it, but some are filled with wind, and others…are dying of hunger through their own folly, while the food is close beside them.

The bread which I shall give is my flesh. As this secret power to bestow life, of which he has spoken, might be referred to his divine essence, he now comes down to the second step, and show that his life is placed in his flesh, that it might be drawn out of it. It is, undoubtedly, a wonderful purpose of God that he has exhibted life to us in the flesh, where formerly there was nothing but the cause of death. And thus he provides for our weakness, when he does not call us above the clouds to enjoy life, but displays it on earth, in the same manner as it he were exalting us to the secrets of his kingdom. And yet, while he corrects the pride of our mind, he tries the humility and obedience of our faith when he enjoins those who would seek life to place reliance on his flesh, which is contemptible in its appearance.

But an objection is brought, that the flesh of Christ cannot give life, because it was liable to death, and because even now it is not immortal in itself; and next, that it does not at all belong to the nature of the flesh to quicken souls. I reply, though this power comes from another source than from the flesh, still this is no reason why the designation may not accurately apply to it. For as the eternal word of God is the fountain of life (John 1:4), so his flesh, as a channel, conveys to us that lifethat dwells intrinsically, as we say, in his divinity. And in this sense it is called life-giving, because it conveys to us that life that borrow for us from another quarter. This will not be difficult to understand, if we consider what is the cause of life — namely, righteousness. And though righteousness flows from God alone, still we shall not attain the full manifestation of it anywhere else than in the flesh of Christ, for in it was accomplished the redemption of man, in it a sacrifice was offered to atone for sins and an obedience to God, to reconcile him to us.  It was also filled with the sanctification of the Spirit, and at length, having vanquished death, it was received into the heavenly glory. It follows, therefore, that all the parts of life have been placed in it, that no man may have reason to complain that he is deprived of life, as it it were placed in concealment, or at a distance.

Excerpt from: PROFILES IN REFORMED SPIRITUALITY - Edited & Introduced by Joel R. Beeke; The Soul of Life: The Piety of John Calvin–Reformation Heritage Books, Grand Rapids, Michigan