For nearly 2000 years the church has celebrated the Lord's Supper, a wonderful gift that Christ has given to us. Yet, how the church has chosen to celebrate the Lord's Supper has varied greatly. The church in Corinth around 51 AD had some issues in their celebrations. They had home meals to accompany their services, but the wealthy among them got to feast on all the food, including the elements of bread and wine, while the poorer among them were left with nothing at all and often went home not only hungry, but without having been given the Lord's Supper.
Paul shares with them that this practice is not good, and then he reminds them what he had taught them when he planted their congregation. In that reminder, Paul shares the words of Jesus that we refer to as the "Words of Institution." These are the words that Matthew, Mark, and Luke also share as they write their Gospel accounts of Jesus' life and ministry.
What I find fascinating is that Paul likely writes these words of Jesus down and sends them to the Corinthians before the Gospel writers compose their books. This teaching was passed down as an oral tradition before the New Testament was even composed.
Not every congregation throughout time and space has included the Words of Institution in their celebrations of the Lord's Supper. Some liturgies from the first few centuries of the early church include other ways of celebrating this sacrament. These ways are not more or less valid that what we do today.
The Words of Institution are not magic. They are not an incantation that turn bread into Christ's body and wine into Christ's blood. The Words of Institution are primarily Jesus' words of promise, words that He speaks in the first celebration of this meal, and words that we echo and repeat when we celebrate this meal. In these words Jesus promises His presence in the meal, a new covenant made by His blood, and forgiveness of our sins.
Our use of the Words of Institution is a bit like a the words a starter uses at a track event. Each time, the starter uses the same motions with the same words. One arm up - "on your marks." Both arms up - "get set." Gun fires. Race ensues.
Likewise when pastors speak the Words of Institution, we use the same words each time. We bless the bread and wine with the sign of the cross. And the celebration ensues.
The difference obviously is that those race directions were not passed down from God Himself. It's not like God officiated the first race and used those exact words. But Jesus Himself does preside over this meal and leads us in a way that we can celebrate it together again and again, always receiving the benefits He promised from the first celebration.