This Supper of the Lord is not limited in its signification to just one or two things. It is richly laden with meaning on multiple levels. But two of them might appear to be in tension.
The Lord’s Supper is a memorial of what Christ has done for us, and the Lord’s Supper is a communion in what Christ has done for us. This Supper is a memorial of the Lord and it is communion with the Lord. In the former sense, it would appear to assume the Lord’s absence, and in the latter sense it would appear to assume the Lord’s presence. Both are true, but in different senses.
The Lord is not present with us physically. His body has ascended into Heaven, and is there, not here. His body was nailed to a tree two thousand years ago, laid in a tomb, and was raised from the grave three days later. That same body ascended into Heaven where it now is. In that sense, this meal is a memorial of His sacrifice for us, reminding us of what He did, as well as a memorial of His sacrifice for God, reminding Him to receive us for Jesus’ sake. In all this, we are presupposing His absence, and we long for His coming again.
But the Lord promised us that if He went away, He would send His Spirit to be present with us. In that sense, because the Holy Spirit of Christ is here with us, Christ is here with us. Christ promised to be wherever two or three are gathered, and so this would certainly include two or three hundred. The Spirit is not only present, but the Spirit is active, knitting us together in love. This is His appointed work, and He does it by creating koinonia or fellowship. Another English word for what is happening in this is communion, which also happens to be a name for the Supper itself.
So Christ is absent, and we remember Him. Christ is present and we commune with Him.
So come, and welcome, to Jesus Christ.