If Christian worship is the communion between God and His people then the Eucharist is the most succinct illustration of that communion, for in it we celebrate God's initiative towards us in the life, death, and resurrection of His Son. We re-enact the meal that Christ celebrated with His disciples shortly before His death on the cross, which was to have fundamental relevance to our lives, for in His body broken for us, and His blood shed for us He broke the power of sin in our lives and gave us the means to a restored relationship with God, and eternal life. In the Eucharist we follow Christ's command to "do this in memory of me" (Luke 22: 19), we remember what God has done for us in Christ, and it becomes real for us in the present. "This means that every time you eat this bread and drink from this cup you proclaim the Lord's death until he comes" (1 Corinthians 11: 26). In the Eucharist we remember more than simply Christ's death, we remember His life and His resurrection and Ascension too.
In the Eucharist we celebrate the new Covenant that Christ came to bring. Before Christ the way to commune with God was through sacrifice. People would offer up sacrifices in order to receive forgiveness and redemption. This had to be done continually. Christ, however, in His death on the cross, became the final sacrifice on our behalf. His blood was shed as the new Covenant, the new way of entering into communion with God. We no longer need sacrifices and High Priests to enter into God's presence, Christ has fulfilled that, and in Him we enter into God's presence, through His body broken, and His blood shed for us. This is vital for our worship of God.
The Eucharist also becomes God's communion with us. Although we are remembering an event that has passed, it also has a present reality for us. As we confess our sins to Him, and partake of the Eucharist, we realise His forgiveness, and experience His redemption as we remember that Christ gave His body and His blood for us and for our forgiveness. The Eucharist becomes a channel of God's grace to us in the present, and His power as He nourishes us to growth. This happens as we interact with Him through these powerful symbols. There has been much controversy around this 'mystery'. Although we do not wish to give the elements themselves the power of transformation, we can not deny that God does use the elements as a means of communicating all that Christ has done for us, and this can be life transforming. God works a change in us as the Christ event is brought to our present reality.
Another area of controversy surrounds the presence of Christ in the Eucharist. Some views hold that the elements actually become the body and blood of Christ, others hold that Christ is only symbolically present. John Wesley adhered to a view between these two, he denied that the elements actually became the physical body and blood of Christ, but he did believe that Christ was present in the Eucharist. For him the real presence of Christ is the Holy Spirit. This is illustrated in the hymn by Charles Wesley:
The Eucharist also points forward to the time when our communion with God will be complete, when we will partake of the heavenly banquet that God has prepared for all those in union with Christ (Luke 14:15, Isaiah 25: 6).
The Eucharist must also thrust us out into the world. As we celebrate God's move towards us, we are forced outward to take Him into all the world.
The Eucharist captures for us God's move towards us, our response to that, and that moves us out into the world to show God to others, it signifies a restored relationship, and communion with God, that is worship, and therefore the Eucharist is central to Christian worship. That is not to say that one can not worship without the celebration of the Eucharist though.