I wish I knew!
To my eyes, this is one of those verses that we must pray to the Spirit for discernment about. I have, but I confess I don't have any insights.
To my eyes, I believe it means that Jesus is saying and stressing in the most profound and powerful language available to him that we must take His teachings and His example and make it part of ourselves. Just as the food we eat and the wine we drink becomes part of our body, I believe Jesus is saying that we must not just "understand" what He says, but rather we must become what He says...
But it certainly is a tough verse.
Mark W.