Scriptural Roots of Holy Communion

Where does the Bible speak of the sacrament of Holy Communion?

The institution of the Eucharist by Christ is described by Matthew, Mark and Luke in their accounts of the Last Supper (Matthew 26:26-29, Mark 14:22-25, Luke 22:19-20). The earliest written account of the institution of the Eucharist is actually found in Saint Paul's First Letter to the Corinthians, composed in or shortly after 50 A.D. This is the passage proclaimed by the Church each year at Holy Thursday mass: 

For I received from the Lord what I also handed on to you, that the Lord Jesus, on the night he was handed over, took bread, and, after he had given thanks, broke it and said, “This is my body that is for you. Do this in remembrance of me.” In the same way also the cup, after supper, saying, “This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me.” For as often as you eat this bread and drink the cup, you proclaim the death of the Lord until he comes. (1 Corinthians 11:23-26)

Note that Jesus twice explicitly tells His apostles: "Do this in remembrance of me.” Jesus did not intend for the Eucharist to be a one-time event exclusively for His apostles, but rather a sacramental celebration for Him to dwell in His faithful ones until the end of the age.

That the Eucharist is truly the Body and Blood of our Lord Jesus is stated very clearly by Jesus Himself in all four of the passages cited above, and is expounded in greater detail by Jesus in the sixth chapter of Saint John's gospel:

Amen, amen, I say to you, unless you eat the flesh of the Son of Man and drink his blood, you do not have life within you. Whoever eats my flesh and drinks my blood has eternal life, and I will raise him on the last day (John 6:53-55). 

Those who do not believe in the Real Presence of Jesus in the Eucharist will sometimes cite John 6:63, where Jesus says, "It is the spirit that gives life, while the flesh is of no avail. The words I have spoken to you are spirit and life." The critical distinction here is between "my flesh" and "the flesh." Jesus says that His flesh ("my flesh") is truly present in the Eucharist and gives eternal life. When He speaks of "the flesh," He is talking about our fallen human nature that is inclined towards sin and needs the graces conveyed by God most abundantly in the sacraments. Jesus warns us about "the flesh" frequently (perhaps most famously when He tells Peter in the garden of Gethsemane, "the spirit is willing but the flesh is weak," Matthew 26:41). 

Pray the Divine Mercy Chaplet every day for the salvation of souls.