The evil whisperings of Satan are abundant, but the most dangerous doubt and suspicion that develops in the heart of man and causes him to lose in this world, as well as in the afterlife, relates to the Hereafter.
For belief in the Hereafter – among other ways and means – is a strong catalyst which moves an individual to perform good and virtuous acts. An individual who considers the Hereafter to be nothing more than a fable or tale, becomes one who is rejected, and loses in this world and the next. This is because awe of the Hereafter also arouses fear in a person, drawing them in towards the true fountain of divine understanding. And divine insight cannot be attained without the awe and fear of God. Hence, remember that when a person begins to doubt the Hereafter, this puts a person’s faith in danger and taints the prospects of a good end.
(Hazrat Mirza Ghulam Ahmadas, Malfuzat, Vol. 1, p. 53)