P. K. Dick's novels are always full of schizophrenia, paranoia and permeating feelings that something is wrong with the universe. In VALIS, this is not just a substanceless feeling but a full-on alarm. The universe is irrational, mad, full of pain and death. There is only one salvation - Zebra. (WTF is Zebra?).
Religion seems to help many people not get mad because of their mortality, and VALIS is Phil's (or Horselover Fat's) take on the view of God (god) and religion. What starts as a simple story about toxic people that can turn even their death against their close ones end in a philosophical tractate, which contains P. K Dick's theophany (experience of God's presence). Which is real life, seems to safe life of its infant son.
To be frank, I think the whole VALIS trilogy is completely mad.... and I love it. The VALIS is P. K. Dick's exegesis of the bible, and it is a unique way how the author's great mind processes its view on religion, meaning of life and life after death. It is not an easy read; religious people will not like the picture of God and the creator of the universe, which P.K Dick is painting, and the rest of us don't have to like the religion. All in all, I think it is a great book, but I think I cannot recommend it to anyone I know.