John Calvin summaries, “our souls are fed by the flesh and blood of Christ in the same way that bread and wine keep and sustain physical life. For the analogy of the sign applies only if souls find their nourishment in Christ—which cannot happen unless Christ truly grows into one with us, and refreshes us by the eating of His flesh and the drinking of His blood.
Even though it seems unbelievable that Christ’s flesh, separated from us by such great distance, penetrates to us, so that it becomes our food, let us remember how far the secret power of the Holy Spirit towers above all our senses, and how foolish it is to wish to measure His immeasureableness by our measure. What, then our mind does not comprehend, let faith conceive: that the Spirit truly unites things separated in space.
Now, that sacred partaking of His flesh and blood, by which Christ pours His life into us, as if it penetrated into our bones and marrow, He also testifies and seals in the Supper—not by presenting a vain and empty sign, but by manifesting there the effectiveness of His Spirit to fulfil what He promises. And truly He offers and shows the reality there signified to all who sit at that spiritual banquet, although it is received with benefit by believers alone, who accept such great generosity with true faith and gratefulness of heart.
In this manner the Apostle said, “The bread which we break, is it not the communion of the body of Christ? The cup of blessing which we bless, is it not the communion of the blood of Christ?” (1 Cor 10:16; order changed). There is no reason for anyone to object that this is a figurative expression by which the name of the thing signified is given to the sign. I indeed admit that the breaking of bread is a symbol; it is not the thing itself. But, having admitted this, we shall nevertheless duly infer that by the showing of the symbol the thing itself is also shown. For unless a man means to call God a deceiver, he would never dare assert that an empty symbol is set forth by Him. Therefore, if the Lord truly represents the participation in His body through the breaking of bread, there ought not to be the least doubt that He truly presents and shows His body. And the godly ought by all means to keep this rule: whenever they see symbols appointed by the Lord, to think and be persuaded that the truth of the thing signified is surely present there. For why should the Lord put in your hand the symbol of His body, except to assure you of a true participation in it? But if it is true that a visible sign is given us to seal the gift of a thing invisible, when we have received the symbol of the body, let us no less surely trust that the body itself is also given to us.