Augustine of Hippo
Catena Aurea · Johannesevangelium 7
In the last day, that great day of the feast, Jesus stood and cried, saying, If any man thirst, let him come unto me, and drink. He that believeth on me, as the Scripture hath said, out of his belly shall flow rivers of living water. (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.)
(Tract. xxxii. 4) The belly of the inner man, is the heart’s conscience. Let him drink from that water, and his conscience is quickened and purified; he drinks in the whole fountain, nay, becomes the very fountain itself. But what is that fountain, and what is that river, which flows from the belly of the inner man? The love of his neighbour. If any one, who drinks of the water, thinks that it is meant to satisfy himself alone, out of his belly there doth not flow living water. But if he does good to his neighbour, the stream is not dried up, but flows.