I don't think most Christian's reasons for going to Church have to do with sin. Most Christians go to Church for fellowship. They go to get a sense of community and belonging, camaraderie and love.
Also they go to be closer to God and receive God's word from their Priest, Minister or Pastor who they see as having wisdom regarding such things.
They also go to worship God and thank him for what he presumably did on the Cross.
Now personally I'm an atheist so I don't think anyone has to go to Church or appease any invisible beings for the things they've done wrong or for any other reasons I stated above. It's especially strange since Jesus who was also supposedly God, only sacrificed himself based on a standard of forgiveness he himself had set up which for some reason involved brutal bloodshed to save us from a punishment he decided on for sins that couldn't possibly have done him any harm (since an immortal perfect being cannot be harmed permanently). The whole thing makes no sense, but people are free to believe it and free to gather together with others who do to enjoy themselves and talk about their shared beliefs.