After Nettles' death, Applewhite also altered his view of ascension; previously, he had taught that the group would physically ascend from the Earth and that death caused reincarnation, but her death—which left behind an unchanged, corporeal body—forced him to say that the ascension could be spiritual. He then concluded that her spirit had traveled to a spaceship and received a new body and that his followers and he would do the same. In his view, the Biblical heaven was actually a planet on which highly evolved beings dwelt, and physical bodies were required to ascend there. Applewhite believed that once they reached the Next Level, they would facilitate evolution on other planets. He emphasized that Jesus, whom he believed was an extraterrestrial, came to Earth, was killed, and bodily rose from the dead before being transported onto a spaceship. According to Applewhite's doctrine, Jesus was a gateway to heaven, but had found humanity unready to ascend when he first came to the Earth. Applewhite then decided that an opportunity existed for humans to reach the Next Level "every two millennia", and the early 1990s would therefore provide the first opportunity to reach the Kingdom of Heaven since the time of Jesus. Zeller notes that his beliefs were based on the Christian Bible, but were interpreted through the lens of belief in alien contact with humanity.