Deepertruth: Jesus appears to St. Thomas Aquinas, Angelic Doctor

The biblical foundation for Holy Communion is what Christ Himself did at the Last Supper. As narrated by St. Matthew, Jesus first offered the apostles what He was about to change, then changed the bread and wine, and then gave them Communion.

And while they were at supper, Jesus took bread and blessed and broke and gave it to His disciples and said, "Take you and eat, this is my Body." And taking the chalice He gave thanks and gave it to them saying, "Drink you all of this. For this is my Blood of the New Testament which shall be shed for many unto remission of sins." (Matthew 26:26-28)

St. John, who does not give us the narrative of the institution of the Eucharist, devotes a whole chapter to Christ's promise of giving His followers His own flesh to eat and His own blood to drink. What Christ emphasizes is the absolute necessity of being nourished by His Body and Blood if the supernatural life received at Baptism is to be sustained.

I tell you most solemnly, if you do not eat the flesh of the Son of Man and drink His blood, you will not have life in you. Anyone who does eat my flesh and drink my blood has eternal life and I shall raise him up on the last day. For my flesh is real food and my blood is real drink. He who eats my flesh and drinks my blood lives in me and I live in Him. As I, who am sent by the living Father, myself draw life from the Father, so whoever eats me will draw life from me. This is the bread come down from heaven; not like the bread our ancestors ate. They are dead, but anyone who eats this bread will live forever. (John 6: 53-58)