Why do Buddhists believe in rebirth?

Answer 1

In the Mahayanic (Great Vehicle) tradition the goal for an enlightened person is to spread the enlightenment among all people. Think of it as "We're all in this together."

As a consequence when an enlightened person is offered the opportunity to enter Nirvana - a state of thoughtless oneness with all the Universes - he will opt to turn it down to return to earth and help others as long as there are unlightened individuals.

The Buddha is enlightened, we aren't, so he returns.

Answer 2

Buddhist believe in rebirth because the first of all believe in the law of cause and effect (karma) which means that nothing exists without a cause. (if there is no seed, there will be no tree)

This law of karma also applies to our consciousness and for a Buddhist consciousness is a stream of moments of consciousness, where each moment is the cause for the next moment. (If I wouldn't be looking at the sky right now, I could not see the cloud moving in the next moment.)

Also, for a Buddhist body and consciousness are separate things. There is some connection between the two but one is material and the other is immaterial.

So, when the material body dies, it doesn't mean that the immaterial consciousness also has to die. Therefore consciousness can continue after the physical death which leads us to rebirth.

In Buddhist history there are many accounts of children that are able to remember things from their past life, stories about near-death experiences and accounts of great meditation masters being able to experience what happens after physical death.

Answer 3

They don't. They believe in Rebirth - which is not quite the same. The belief in rebirth is part of a cyclical world-view.