The Lord's Supper is the most regular sacrament. Baptism being the other, and it only being celebrated when someone professes turning to Jesus Christ in faith for the forgiveness of sins. The Lord's Supper is a formational element of worship. In it, we proclaim Christ's death until he comes again (1 Corinthians 11:26).
In Communion, with whom do we commune? Do we really commune? "This is my body" "This is my blood" so Jesus said. I do not intend to debate regarding the meaning of the linking verb--doctrines should not be built on such by themselves. Look, rather, at what follows. The blood is the blood of the covenant. It is the blood by which we are brought into a covenantal relationship with God. The body of Christ, broken for us on the cross is that body to which we are joined by the Holy Spirit.
Let us try the idea that the Lord's Supper is merely a representation, that the cup merely signifies Christ's blood, and that the bread merely signifies his body. Okay, I'm a bit of a philosophy geek, so the question I am inclined to ask is, "what does it mean that A signifies B?" And plenty has been written about signifiers, but let me just point out two things:1. words are signs, they signify, as it were, meanings (and the Wittgensteinian in me requires that I put caution tape around that word, "meaning"--a word by itself means nothing, it only means things in contexts) 2. we eat our words when we want to take back what we mean. Conclusion? Signs basically are, or at least may be treated the same as, what they signify. If the cup signifies Jesus Christ's blood, poured out for the forgiveness of sins, then, when I drink of it, I am engaged in drinking the blood of Christ. I do not mean this in any metaphysically weird way, as in transubstantiation, nor is it necessary to invoke Christ's infinite spiritual body and blood, nor need we say that the Spirit spans the distance between us and heaven so that Christ's body and blood are present in that way. Simply because the bread and the cup signify Christ's body and blood, we are partaking of Christ's body and blood, receiving from his death. And since God has ordained this sacrament, so that the signification is, necessarily, true, that is, what we say by partaking of the elements is true, we will receive from his death either the benefits or the curse thereof. The benefit is communion with God, received by faith; the curse is judgement (1 Corinthians 11:29).
It is sometimes said that Christianity is not a religion, but a relationship. By that it is meant that in Christianity we have a person rather than rules. This seems like an odd dichotomy, for people give rules, after all. Growing up, was my being-raised a relationship or rules? Certainly the former, and the latter would have been worthless at best without the former, but both existed. I was raised in a relationship partially structured by rules. The Lord's Supper is something we are commanded to do, and it is one of those things which appears most religious about Christianity. It is also one of the focal points of the relationship of Christianity.
Finally, who should receive the Lord's Supper? From 1 Corinthians 11:28 we have: only the one who examines himself and from the nature of the act we know that only the one who professes faith ought to partake of it, lest we encourage lying. This latter entails that only the baptized should receive communion, for all those who have professed faith should be baptized. Lastly, we know that all of those who so qualify and are present should receive both the bread and the cup since Jesus says "Drink of it, all of you" Matthew 26:27, and since nowhere is a distinction made between those who receive the bread and those who receive the cup, but rather those who should desire to drink the cup are those who know that they need the blood shed for the forgiveness of sins, and those who should desire the bread are those who desire to remember Christ, and both are said to proclaim Christ's death until he comes again, by Paul. Therefore, as those who would proclaim Christ's death unto life to a dying world, we should desire to partake of communion often. We should feel denied our right as Christians if ever communion is served and we are retrained without good reason from partaking of it. We should care because we want to be those who proclaim Jesus's death to the world until he comes again.