For Jewish people this teaching was most certainly a hard pill to swallow. It says just a few verses later that many of His followers left Him after He taught this (Jn.6:66). For Jewish people were well aware that their law taught them that they were never even to eat meat if it still had the blood in it.
“‘And whatever man of the house of Israel, or of the strangers who dwell among you, who eats any blood, I will set My face against that person who eats blood, and will cut him off from among his people. For the life of the flesh is in the blood, and I have given it to you upon the altar to make atonement for your souls; for it is the blood that makes atonement for the soul.' Therefore I said to the children of Israel, 'No one among you shall eat blood, nor shall any stranger who dwells among you eat blood.' Whatever man of the children of Israel, or of the strangers who dwell among you, who hunts and catches any animal or bird that may be eaten, he shall pour out its blood and cover it with dust; for it is the life of all flesh. Its blood sustains its life. Therefore I said to the children of Israel, 'You shall not eat the blood of any flesh, for the life of all flesh is its blood. Whoever eats it shall be cut off’” (Lev. 17:10-14).
Eating blood was strictly forbidden in the Old Testament, and whoever ate it would be “cut off.” So we can rule out that the Lord was speaking literally.
When I was in leadership in a Messianic Jewish congregation years ago, I knew a gentile man who was very legalistic about keeping the Old Testament law. (Many gentiles in Messianic congregations want to go back to the O.T. law. I am not one of them; I strive to live by the Spirit). Of course, he kept strict Old Testament dietary laws as most people who go to Messianic synagogues do. This man would have never broken the law by eating blood or pork. Being of Scottish descent, he had always wanted to visit Scotland. He finally was able to go; and when he got back, he told me the story of how much he was getting back to his roots and enjoying their traditional “black pudding.” He just could not get enough of it. After several days of eating it, he finally asked a waitress what it was made from. She answered, “Pig’s blood and oatmeal.” The man got sick on the spot and had to get out of there as fast as he could. Weeks later he got nauseous telling me about it. Oh, how I laughed for days!
Earlier in John chapter six Jesus had said about the manna the Israelites ate in the desert,
"Most assuredly, I say to you, Moses did not give you the bread from heaven, but My Father gives you the true bread from heaven. For the bread of God is He who comes down from heaven and gives life to the world." Then they said to Him, "Lord, give us this bread always." And Jesus said to them, "I am the bread of life. He who comes to Me shall never hunger, and he who believes in Me shall never thirst (John 6:32-35).
So in this chapter Jesus is comparing the literal bread that came from heaven and nourished the Israelites with Himself being a type of spiritual bread that will nourish the souls of His disciples. Bread is a type of word of God in the Bible. So one of the things He meant by eating His flesh is accepting His words as the “living bread” (Jn. 6:51). Jesus actually clarified what He meant in just a few sentences later,
"Does this offend you? What then if you should see the Son of Man ascend where He was before? It is the Spirit who gives life; the flesh profits nothing. The words that I speak to you are spirit, and they are life (John 6:61-63).
He says here that His words are “spirit and life,” making clear He was speaking spiritually concerning His words. However, Paul brings out another application of eating His flesh. He said,
The bread which we break, is it not the communion of the body of Christ? For we, though many, are one bread and one body; for we all partake of that one bread (1 Cor. 10:16-17).
We know that the literal body of Christ was never broken (Jn. 19:36). Paul says that we who are believers are the body of Christ—the loaf broken into many pieces. He also says in several places that we are to edify one another. For example:
Therefore let us pursue the things which make for peace and the things by which one may edify another (Rom. 14:19).
How is it then, brethren? Whenever you come together, each of you has a psalm, has a teaching, has a tongue, has a revelation, has an interpretation. Let all things be done for edification (1 Cor. 14:26).
Therefore comfort each other and edify one another, just as you also are doing (1 Thess. 5:11).
So then we who are the “loaf” and “body of Christ” are to feed one another the bread of life for nourishment. This is the real meaning of communion. In churches we almost never see the members edifying one another. It is usually one person edifying the rest once a week.
Now that we see what He meant by “eating His flesh,” lets examine what He really meant by drinking His blood.
Jesus said on the night of the last supper,
Then He took the cup, and gave thanks, and gave it to them, saying, "Drink from it, all of you. For this is My blood of the new covenant, which is shed for many for the remission of sins (Matt. 26:27-28).
His blood was His sacrifice for the new covenant for the remission of sins. Covenants in the Old Testament were sealed in blood.
Therefore not even the first covenant was dedicated without blood. For when Moses had spoken every precept to all the people according to the law, he took the blood of calves and goats, with water, scarlet wool, and hyssop, and sprinkled both the book itself and all the people, saying, "This is the blood of the covenant which God has commanded you." Then likewise he sprinkled with blood both the tabernacle and all the vessels of the ministry. And according to the law almost all things are purified with blood, and without shedding of blood there is no remission (Heb. 9:18-22).
To drink of His blood is to come into the new covenant via the spirit for cleansing from sin and for sanctification. For it is through His blood we are forgiven of our sins and filled with His Spirit. It is by His Spirit that we are sanctified. Wine is a symbol of blood and spirit.
. . . who also made us sufficient as ministers of the new covenant, not of the letter but of the Spirit (2 Cor. 3:6).
So then, when Jesus said that you must eat His body and drink His blood, he was speaking of the blood of the new covenant which is implemented by the Spirit and His body, which is His word, including anointed words given by a multi-membered body to edify one another.