1 Corinthians 10:17

We being many, are one bread. Or, as it may be rendered, agreeably both to the Latin and Greek, because the bread is one, all we, being many, are one body, who partake of that one bread. For it is by our communicating with Christ and with one another, in this blessed Sacrament, that we are formed into one mystical body; and made, as it were, one bread, compounded of many grains of corn, closely united together. (Challoner) --- From the sacrament of the real body of Christ in the eucharist, he passeth to the effect of this sacrament, which is to unite all those who partake of it, as members of the same mystical body of Christ, which is his Church: and from hence he presently draws this consequence, that such as are members of that body, of which Christ is the head, cannot have any communication with idolaters, or with those that offer sacrifices to idols and devils. (Witham)