Christians tend to gather on Sunday, because it is the Lord's Day - the Day Christ rose from the dead. But what do we gather for? Why do we come together?
Christians come to be in the presence of their Lord, and we believe that Jesus is present with us in His Word and Sacrament. And not just in the "He lives in my heart" sense - but in the real sense - in a reality we perceive by faith. We know He is there to give us His gifts - forgiveness of sins, life and salvation. We know He is there to wash us in Baptism, speak promises to us in His Word and feed us in His Supper. We gather to be with Jesus.
This is why the earliest Christians always celebrated the Lord's Supper every time they gathered. It was why they gathered, because they believed that Jesus - their Lord who had ascended into heaven - was present with them in this Supper He instituted for His Church. This is the most substantial way He comes to be with His people.
Think of the Lord's Supper as a kiss shared by husband and wife. The minute you have to place rules on how often, the kiss loses its affectionate force. But no one would ever say, "I think we have kissed enough," or "That kiss will have to do for the rest of the day." No one says, "How often do we have to kiss?" Instead we ask, "How often do we get to kiss?" Let's face it, we kiss and get kissed as often as we can (at least when there is peace...hehe).
And with Christ there is ALWAYS peace. Because the Lord's Supper is more than a kiss from God. It isn't merely something we want - it is something we need. It is the forgiveness of sins, life and salvation in, with and under the body and blood of Jesus Christ. It is God's New Testament for His people - His New Covenant Promise that we are reconciled - and this reconciliation - this Oneness - is in the blood of His Son. So let us not ask, "How often do we have to commune with our Lord?" But "How often do we get to commune with our Lord?"