1. There is no good reason to not believe in life after death. There is no proof against it.
2. Agrument from authority. If millions of people believe in life after death there is a smaller chance that they are wrong. Almost every culture has come to belive that there is life after death. Jesus' main message was that there is life after death.
Conservation of energy. Matter cannot be created or destroyed, so the preservation of our soul agrees with this
The Nature of Man. One can see a clear difference between something that is alive and dead. This difference is the presence of the soul in the body. The soil must leave the body when the being dies.
The Nature Of God: God must have created an afterlife for us, otherwise there would be no reasn fro creating us at all.