He uses the analogy of the 2 clocks to illustrate his point. God is seen the master craftsman who has created 2 clocks of such perfection that they always show the same time. Whilst this point of view does not rule out immortality, it does seem that free will can not exist as god has pre-established all possible activities. For example if I think that I want some chocolate, this may be because my stomach is sending messages to the brain because my blood sugar level is low. For an epiphenomenalist consciousness has no power to cause anything, it is simply a reflection of biology, and of course when the body dies, the mind dies with it.
Recent philosophers are interested in the possibility of artificial intelligence.
He did think that it was possible to doubt the existence of his body. Many times he had dreams, which when he awoke he found to have no basis in reality. He imagined that a malicious demon might be fooling him into believing that he had a body. Later he argues that God exists and that as God exists he can be fairly sure that his body exits also. Mind is conscious and non-spatial and body is spatial but not conscious.