8 Let us run then, my brethren, let us run, and love Christ. What Christ? Jesus Christ. Who is He? The Word of God. And how came He to the sick? “The Word was made flesh, and dwelt in us.” It is complete then, which the Scripture foretold, “Christ must suffer, and rise again the third day from the dead.” His body, where is it? His members, where toil they? Where must you be, that you may be under your Head? “And that repentance and remission of sins be preached in His name through all nations, beginning at Jerusalem.” There let your charity be spread abroad.
Christ says, and the Psalm, i.e. the Spirit of God, “Your commandment is exceeding broad:” and forsooth some man will have charity to be confined to Africa! Extend your charity over the whole earth if you will love Christ, for Christ's members are over all the earth. If you love but a part, you are divided: if you are divided, you are not in the body; if you are not in the body, you are not under the Head. What profits it you that you believe and blaspheme? Thou adorest Him in the Head, blaspheme Him in the Body.
He loves His Body. If you have cut yourself off from His Body, the Head has not cut itself off from its Body. To no purpose do you honor me, cries your Head to you from on high, to no purpose do you honor me. It is all one as if a man would kiss your head and tread upon your feet: perchance with nailed boots he would crush your feet, while he will clasp your head and kiss it: would you not cry out in the midst of the words with which he honors you, and say, What are you doing, man?
You tread on me. You would not mean, Thou treadest on my head; for the head he honored; but more would the head cry out for the members trodden upon, than for itself because it was honored. Does not the head itself cry out, I will none of yours honor; do not tread on me? Now say if you can, How have I trodden upon you? Say that to the head: I wanted to kiss you, I wanted to embrace you. But do you not see, O fool, that what you would embrace does in virtue of a certain unity, which knits the whole frame together, reach to that which you tread upon?
Above you honor me, beneath you tread upon me. That on which you tread pains more than that which you honor rejoices. In what sort does the tongue cry out? “It hurts me.” It says not, “It hurts my foot,” but, “It hurts me,” says it. O tongue, who has touched you? Who has struck? Who has goaded? Who has pricked? No man, but I am knit together with the parts that are trodden upon. How would you have me not be pained, when I am not separate?
Source: Homilies on the First Epistle of John (New Advent)