For I received from the Lord what I also delivered to you, that the Lord Jesus on the night when he was betrayed took bread, and when he had given thanks, he broke it, and said, “This is my body which is for you. Do this in remembrance of me.” In the same way also he took 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 Lord’s death until he comes.
(1 Corinthians 11:23-26 ESV)
Paul and the apostles learned from Jesus. Broken bread to remember a broken body. A cup of wine to remember spilled blood.
They taught it to the earliest believers and to the leaders of the churches they started.
And they devoted themselves to the apostles’ teaching and the fellowship, to the breaking of bread and the prayers. (Acts 2:42 ESV)
They continued to teach the churches, recording their instructions in one of the earliest written works, The Didache.
Now about the Eucharist: This is how to give thanks: First in connection with the cup: “We thank you, our Father, for the holy vine of David, your child, which you have revealed through Jesus, your child. To you be glory forever.”
Then in connection with the piece [broken off the loaf]:
“We thank you, our Father, for the life and knowledge which you have revealed through Jesus, your child. To you be glory forever.
Through the centuries, it came to be practiced less often, but still those who knew taught the new believers about the bread and the cup.
Through schism and reformation, denominational splits and Great Awakening, the teaching passed from believer to believer.
Churches may believe differently about what communion is – whether the bread and the wine actually becomes the body of Christ or if it is symbolic, whether it’s something to be practiced routinely or just on occasion.
But at some point when they gather, the bread is broken and the cup is passed.
We remember our unity with the believers who came before us.
We proclaim the Lord’s death until he comes.