John 6 & 7

When Jesus called himself the "bread of life," he was using a rich symbol of Jewish life.

Bread was an important part of Israel's worship. During the celebration of Pentecost, two loaves of leavened bread were offered as sacrifices. In the tabernacle, and later in the temple, the Levites placed twelve loaves of unleavened break, or bread without yeast, before the Lord each week to symbolize God's presence with the twelve tribes.

Animal sacrifice was also common in the ancient world. During a sacrifice a token part of the animal was burned on the altar, although the whole animal was offered to the god. Part of the flesh was given to the priest to use as they wished, and part went to the worshipper to make a feast for himself. At that feast the god himself was thought to be a guest. Once the flesh had been offered to the god, it was believed that he had entered into it; therefore when the worshipper ate it he was literally eating the god. When people finished such a feast they believed themselves to be literally god-filled.

So John's readers would not have been shocked by the idea of eating Christ's body and drinking His blood. They would have quickly understood the experience of union that communion represents.