Jesus clarifies the meaning of this phrase later in chapter 6
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Then many of his disciples who were listening said, “This saying is hard; who can accept it?”
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Since Jesus knew that his disciples were murmuring about this, he said to them, “Does this shock you?
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What if you were to see the Son of Man ascending to where he was before?
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It is the spirit that gives life, while the flesh is of no avail. The words I have spoken to you are spirit and life.”
The eating of Jesus flesh is a spirtual action. Which is not to say that it isn’t very real. Spirtual matters are in fact more important than physical matters. Elsewhere in chapter 6 Jesus says:
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“Do not work for food that perishes but for the food that endures for eternal life, which the Son of Man will give you. For on him the Father, God, has set his seal.”
So what is this food? In chapter 4 Jesus talks about the food that he eats - while his disciples are trying to get him to eat ‘regular’ food
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Meanwhile, the disciples urged him, “Rabbi, eat.”
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But he said to them, “I have food to eat of which you do not know.”
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So the disciples said to one another, “Could someone have brought him something to eat?”
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Jesus said to them, "My food is to do the will of the one who sent me and to finish his work.
I think that is probably the clearest explaination of what it means to “eat the flesh of Jesus”
Just as Jesus was fed and sustained by doing the will of God, we are called to feed on him by keeping the commandments he left us. If we follow the path Jesus showed us. We are feeding on him.
-Jim