Albert Barnes on 1 Corinthians 10:17

For we. We Christians.

Being many. Greek, The many. οιπολλοι. The idea is not, as our translation would seem to indicate, that Christians were numerous, but that all (for οιπολλοι is here evidently used in the sense of παντες, all) were united, and constituted one society.

Are one bread. One loaf; one cake. That is, we are united, or are one. There is evident allusion here to the fact that the loaf or cake was composed of many separate grains of wheat, or portions of flour united in one; or, that as one loaf was broken and partaken by all, it was implied that they were all one. We are all one society; united as one, and for the same object. Our partaking of the same bread is an emblem of the fact that we are one. In almost all nations the act of eating together has been regarded as a symbol of unity or friendship.

And one body. One society; united together.

For we are all partakers, etc. And we thus show publicly that we are united, and belong to the same great family. The argument is, that if we partake of the feasts in honour of idols with their worshippers, we shall thus show that we are a part of their society.

(*) "one bread" "Loaf"