Why are dead people buried in coffins instead of without?

I know people want to say "to give a proper burial" or so to "make the dead comfortable". Really all the coffin is is a box. The dead won't be comfortable because they are dead not alive. They won't feel anything. Plus a beautiful coffin won't make being dead easier on the spirits of the dead people and it won't insure the people get into Heaven. Also the dead won't use the coffins as beds or boats in the afterlife. So why was this tradition started?