While teaching in the synagogue (see John 6:51-58) Jesus gave a shocker of a sermon. Eat my flesh and drink my blood, he said. The very idea of drinking any blood, let alone human blood, was repugnant to the religious leaders—the law forbid it. The Jewish audience was mad, they had heard enough, they were especially upset about the implications of what Jesus was saying. In the ritual purity laws established in Leviticus, contact with some sources of uncleanness is prohibited, and with others, there is a procedure for cleansing.
The belief is this—a violation of these laws meant that God’s presence in the midst of his people would no longer exist; they would be cut off from God. Therefore, what is unclean is an abomination to God and will not be tolerated. Of the violations, "blood must not be eaten,” was among the most serious.
To the Jewish mind eating the blood of an animal was serious enough, so when they heard Jesus saying “whoever eats my flesh and drinks my blood has eternal life,” to them, the very suggestion of drinking “human blood” was unthinkable—it was blasphemy!
In their minds what they likely heard Jesus saying was: “Eat my flesh and be cut off from God; drink my blood and God’s presence will no longer exist in your life.” What a horrifying thought. No wonder they were so upset. Unfortunately they also missed out on one of the points Jesus was trying to make.
The point, William Barclay suggests:
“To eat Christ’ body is to feed on the thought of who he was,
until we ourselves are fortified, cleansed and transformed by who he is.”
The real shocker Jesus told his audience that day in the synagogue was not that we should (or would) literally be eating his flesh and drinking his blood… but that we should have a diet which consist of feeding and filling our hearts, souls, and minds with who he was in order to be transformed because of who he is—bread that has come down from heaven—blood spilled on a cross that washed our sins away.