Since a christian can repent at home, what is the absolute reason why they have to go to church... (see below)

Church is for fellowship and for added strength. God teaches in 1 Corinthians 12 that we are all members of the body of Christ. Just as we need each the parts of our body to function our best, spiritually, we all function our best when we have the support of others. we don't need a church to be saved, but it sure helps to have a group of people who are like minded to support and strengthen one another.