Augustine of Hippo — as excerpted in the Catena Aurea on John 6:28-34

“(xxv. 12) To eat then that meat which endureth unto everlasting life, is to believe on Him. Why dost thou make ready thy tooth and thy belly? Only believe, and thou hast eaten already. As He called on them to believe, they still asked for miracles whereby to believe; They said therefore unto Him, What sign shewest Thou then, that we may see and believe Thee? What dost Thou work?”