Augustine of Hippo — as excerpted in the Catena Aurea on John 6:60-71

“(Tr. xxvii) If then thou understandest them spiritually, they are life and spirit to thee: if carnally, even then they are life and spirit, but not to thee. Our Lord declares that in eating His body, and drinking His blood, we dwell in Him, and He in us. But what has the power to affect this, except love? The love of God is shed abroad in our hearts by the Holy Spirit, which is given to us. (Rom. 5:5)”