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We often find people complaining that why there is so much suffering and pain in this world which is governed by an Ever-Merciful God who loves His Creation. It is in His Infinite Wisdom that He created all these to maintain an intricate balance. Afterall suffering is but the absense of happiness just as shade is the absence of light.

To get a very insightful account on the subject, read the Chapter ” The Question of Suffering” from the book “Revelation, Rationality, Knowledge and Truth”,    written by Hazrat Mirza Tahir Ahmad(r.a), the fourth successor of the Promised Messiah(a.s)

     http://www.alislam.org/library/books/revelation/part_2_section_6.html