We must believe that God exists and that He rewards those who seek Him
Matthew 6:6 (ASV)
6But thou, when thou prayest, enter into thine inner chamber, and having shut thy door, pray to thy Father who is in secret, and thy Father who seeth in secret shall recompense thee.
Hebrews 11:6 (ASV)
6and without faith it is impossible to be well-pleasing unto him; for he that cometh to God must believe that he is, and that he is a rewarder of them that seek after him.