There will be no sin in heaven! No one will accidentally end up in heaven. One must plan to be there or will end up like the rich man; read Luke 16:19-23!
Back to what Jesus said, "He that eateth my flesh and drinketh my blood, dwelleth in me and I in him." What does this statement make you think of? It should be the Lord's Supper! This was the last get-together that Jesus spent with the 12 before he died, showing how they were to remember Him. God would raise Him from the dead on the 3rd day, Sunday, and the empty tomb would prove Him to be the only man ever raised to never die again. Even Mohammed's bones are still in his grave. Jesus's tomb is empty!
Thus this living memorial is very important to keep every first day of the week, and you say, "it doesn't say every," but remember the Sabbath day? It didn't say "every." When the seventh day came, they kept it! When the first day comes, we should celebrate the Lord's Supper! More than one purpose is assigned to the Lord's Supper. It is a communion, 1 Corinthians 10:16-7. It is a memorial, 1 Corinthians 11:23-5, and last of all, it is a sermon which we preach to others as Jesus said, "For as often as ye eat this bread and drink the cup, ye proclaim the Lord's death till he come," verse 11:26.
Some teach the emblems, bread, fruit of the vine change to be the actual body and blood of Jesus, but this is not so, as the items are emblematic. God has done His part for our salvation. Have you done your part to make your salvation sure? What is your part? Does the Bible tell us?