St. John, in Chapter Six of his Gospel, developed two ways in which Jesus is the Bread of Life.
First, John quoted Jesus as saying He himself was the Bread of Life come down from heaven.
Secondly, John quoted Jesus as saying the bread that he would give us is his life which he gives to us.
Let me transfer to another matter, namely to the question as to how the Mass can be a sacrifice. Now, the only sacrifices known to the ancient world were ones in which the victim was brought to death. And so, Christians debated on ways that the death of Jesus was part of the Mass.
However, St. Augustine, put aside the element of death in our Masses. He said that the sacrifice of the Mass consists in Jesus and his followers giving God their complete love and obedience. To grasp this point we must see how the Last Supper followed the customary formula for such ritual dinners.
That ritual divided the table bless into three parts. In the first, the diners recalled all of God's favors to them. In the second part they reminded theirselves that they were living in God's presence. The third part had the host and the diners making themselves into one pleasing gift to God in return for his may favors to them. The Greek word for Pleasing Favors was Eucharist.
Both St. Paul and St. Luke in their account of the Consecration at the Last Supper tell us that it was at that their part of the table blessing, at the Eucharist, that Jesus said, "This is my body which is for you." He is there asking you and I to become part of his one Eucharist that he offers to the Father as an act of obedience and life.