Let's first look at why God allows suffering. We know that man was created perfect and dwelt in the Garden of Eden in harmony with God. Adam succumbed to the temptation to sin and fell out of harmony with God. As part of his punishment, suffering, and eventually death, upon all of mankind was permitted by God. Genesis 3:16,17 reads, "Unto the woman he said, I will greatly multiply thy sorrow and thy conception; in sorrow thou shalt bring forth children . . .

And unto Adam he said, Because thou hast hearkened unto the voice of thy wife, and hast eaten of the tree, of which I commanded thee, saying, Thou shalt not eat of it: cursed is the ground for thy sake; in sorrow shalt thou eat of it all the days of thy life." 

We also know that God provided an avenue for mankind to be restored to a full, perfected relationship to him through his son. John 3:16, "For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life."  In paying the price for Adam's sin, Christ also was caused to suffer, 1Peter 3:18,  "For Christ also hath once suffered for sins, the just for the unjust, that he might bring us to God . . . "   Through Christ's suffering, we are brought back to perfection.  Further assurances are given to us through the prophet Isaiah that sorrow will end.  Isaiah 51:11 reads,  "Therefore the redeemed of the LORD shall return, and come with singing unto Zion; and everlasting joy shall be upon their head: they shall obtain gladness and joy; and sorrow and mourning shall pass away." 

There has been, and continues to be, much suffering due to this fall from man's perfected state.  God permits Satan to have his influence during this period of man's history so that man will learn the consequences of sin. Romans 6:23  "For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord."  

Yet, we are assured that man's sorrow will not last indefinitely. Once mankind is renewed to the perfected state in which he was created, he will gradually come back into harmony with God. Satan, and his negative influences, will also be gradually bound. This occurs during  Christ's 1,000 year reign. Mankind will be given ample opportunity to come into harmony with righteousness.  At the end of this 1,000 year period, man's happiness will be complete and everlasting. God has promised us in Revelation 21:4 that,  “…God shall wipe away all tears from their eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away."