It is a reminder of who Jesus is and what he did for us because of his love for us. Because of the work Jesus accomplished by the breaking of his body and the shedding of his blood the way has been opened for us to have the kind of relationship few men had ever enjoyed with God up until the time of his sacrifice. I don't think the meaning has ever changed; but our understanding of it has changed. I don't think we get it. When Jesus said drink all of it I believe he meant drink in everything contained in this cup. Not just the wine (or juice) but the removal of the curse of sin. Drink everything his blood was designed to do for us. We cannot really understand the design unless we look to the designer.