The Real Presence and Holy Sacrifice of Jesus Christ in the Eucharist.
He that eateth my flesh, and drinketh my blood, hath everlasting life: and I will raise him up in the last day. For my flesh is meat indeed: and my blood is drink indeed. He that eateth my flesh, and drinketh my blood, abideth in me, and I in him. As the living Father hath sent me, and I live by the Father; so he that eateth me, the same also shall live by me. This is the bread that came down from heaven. Not as your fathers did eat manna, and are dead. He that eateth this bread, shall live for ever.
Gospel of St. John 6:54-58