<human>:  Why did the historical Buddha have to be reborn?
<bot>: The historical Buddha was reborn many times because he had not attained enlightenment. In order to attain enlightenment, one must first be born into a human body. The Buddha then spent many lifetimes practicing meditation and other spiritual practices in order to become enlightened. The Buddha did not attain enlightenment until he had attained Nirvana. Nirvana is the highest state of enlightenment, and is defined as the complete extinction of suffering.