If you accept multiple lifetimes, everything that we have here will be lost emoment this body goes. We are quite helpless in that case, then only spirituality can rescue us. It's not enough just to say it will overcome suffering in this life and that's it. No, deep if you think more deeply, it is important to believe in in this cycle of birth and death. That is the traditional way in which spiritualitiis taught in all these ancient systems.
Swami Sarvapriyananda teaches the Katha Upanishad, which is one of the most popular Upanishads. The scripture concerns the story of a young man who goes to the house of death to find out what happens after death. The reply describes the nature of reality and the meaning of life.