And he took bread, and when he had given thanks, he broke it and gave it to them, saying, “This is my body, which is given for you. Do this in remembrance of me.” And likewise the cup after they had eaten, saying, “This cup that is poured out for you is the new covenant in my blood. (Luke 22:19-20)
For people in churches up and down the country, communion is probably one of the most misunderstood things that they do. Some go through the motions and others fake emotion. Some think it's only for the really serious Christians, others don't take it because they've had a bad week and feel far from God. Some think that taking it makes God happy with them again. For this reason, it's important that churches don't assume everyone understands what's going on and explain what's happening every time. It's not difficult to explain, Jesus does it here in a few sentences.
We do it to remember what he's done. To remember he gave his body for us. To remember that our sins have been washed away, for good, by his sacrifice of blood. The person going through the motions needs to remember why that's a big deal. The emotional faker needs to remember this to feel the deep remorse over their sin and the deeper joy of forgiveness. The super-christian and the doubting struggler can both take it together and remember that their salvation depends on Jesus sacrifice, not on their performance. The superstitious person needs to remember that God delights in them because of Jesus, not because they've never missed the Lord's supper this year.
Do this in remembrance of me. Let's not forget to remind people of what they are remembering.