In order to believe the teaching, in order to change your life and fulfill the teaching, external proofs are unnecessary. One does not need the promise of rewards, but a clear understanding of what true life is. If people think they can be all-powerful masters of life, that life is given to them for the lusts of the flesh, then it is obvious that every act of sacrifice for another will seem to them a deed worthy of a reward and without reward they will not do anything.
