Christ appointed the two forms of bread and wine, rather than any other, as a further indication of the very union and fellowship which is in this sacrament. For there is no more intimate, deep, and indivisible union than the union of food with him or her who is fed. For the food enters into and is assimilated by our very nature, and becomes one substance with the person who is fed.
Other unions, achieved by such things as nails, glue, cords, and the like, do not make one indivisible substance of the objects joined together.
Thus in the sacrament we too become united with Christ, and are made one body with all the saints, so that Christ cares for us and acts in our behalf. As if he were what we are, he makes whatever concerns us concern him as well, and even more than it does us.
In turn we so care for Christ, as if we were what he is, which indeed we shall finally be — we shall be conformed to his likeness. As St John says, “We know that when he shall be revealed we shall be like him” (1 John 3:2).
So deep and complete is the fellowship of Christ and all the saints with us. Thus our sins assail him, while his righteousness protects us.
For the union makes all things common, until at last Christ completely destroys sin in us and makes us like himself, at the Last Day. Likewise by the same love we are to be united with our neighbours, we in them and they in us.