Institutes of the Christian Religion

“Therefore, if, by the breaking of the bread, the Lord truly represents the participation of his body, it ought not to be doubted that he truly presents and communicates it. And it must always be a rule with believers, whenever they see the signs instituted by the Lord, to assure and persuade themselves that they are also accompanied with the truth of the thing signified. For to what end would the Lord deliver into our hands the symbol of his body, except to assure us of a real participation of it? If it be true that the visible sign is given to us to seal the donation of the invisible substance, we ought to entertain a confident assurance, that in receiving the symbol of his body, we at the same time truly receive the body itself.”