It can get to be a fine line sometimes to understand things.
Now the first thing to understand is that the Lord's Supper is the visible Gospel. When you think of it, the whole Gospel is there rolled into a short rite. Here is Jesus' body given for you, Here is Jesus' blood shed for you. And the participation with faith is really the acceptance, the belief that the Gospel is true. Those that really claim is is nothing but a memorial really do not do it justice, for how can one accept the Gospel as true and have it be nothing?
Anyway on to the real presence. Many take John 6 as teaching the real presence but that was before the Lord's Supper was instituted, it's a bit of a stretch to take it literally especially when the passage seems internally to be pointing to a figurative meaning.
But the real presence is indeed taught, actually demanded of people.
1Co 10:15-17 NET.
(15) I am speaking to thoughtful people. Consider what I say.
(16) Is not the cup of blessing that we bless a sharing in the blood of Christ? Is not the bread that we break a sharing in the body of Christ?
(17) Because there is one bread, we who are many are one body, for we all share the one bread.
Note that the questions are really the same in Hebrew, they demand an affirmative answer from the reader. Is not the cup a sharing in the blood-yes. Is not the bread a sharing in the body-again yes.
The reason that it is so important that the bread is indeed his body is given in verse 17. It unites his people into one body, the body of Christ, his church. Can bread do such a thing, no, no bread can do it, only through the body of Jesus can such a unity be created. It's really the same thing that we are being taught when we are told we cannot be united to idols and to God.
As for the blood, that's really taught elsewhere. Basically the thing is that the blood contains the life. You see this teaching throughout the Bible. And when we receive Jesus' blood we receive his life.
Now some people want to go too far and say that is cannibalism. Well, maybe that case could be made for transubstantiation, but the Bible doesn't teach transubstantiation. If you notice in the passage above, it is still referring to for instance the bread, the bread is not gone. But the bread and wine are united with Jesus' body and blood in a supernatural, sacramental union. We do not know exactly how this all works, but we accept it because it is what the Bible tells us.
It can seem like cannibalism, but that is a rather crude understanding. And it's not just a memorial, that's rather crude as well. The thing is to maintain the correct stance as taught by scripture without falling off either way, which is somewhat difficult but then we were never told the path was wide and easy to follow were we?
Hope that helps.
Marv