"The course of our mortal life, from birth to death, conforms to eternal law and follows a plan described in the revelations as The Great Plan of Happiness. The one idea, the one truth I would inject into your minds is this: There are three parts to the plan. You are in the second or the middle part, the one in which you will be tested by temptation, by trials, perhaps by tragedy. Understand that, and you will be better able to make sense of life and to resist the disease of doubt and despair and depression...
The plan of redemption, with its three divisions, might be likened to a grand three-act play. Act I is entitled 'Premortal Life.' The scriptures describe it as our First Estate. Act II, from birth to the time of resurrection, the 'Second Estate.' And Act III, 'Life After Death or Eternal Life.'
In mortality, we are like one who enters a theater just as the curtain goes up on the second act. We have missed Act I. The production has many plots and sub-plots that interweave, making it difficult to figure out who relates to whom and what relates to what, who are the heroes and who are the villains. It is further complicated because you are not just a spectator; you are a member of the cast, on stage, in the middle of it all!
...Until you have a broad perspective of the eternal nature of this great drama, you won’t make much sense out of the inequities in life. Some are born with so little and others with so much, some in poverty, with handicaps, with pain, with suffering, premature death even of innocent children. There are the brutal, unforgiving forces of nature and the brutality of man to man. We’ve seen a lot of that recently."
Do not suppose that God willfully causes that, which for His own purposes, He permits. When you know the plan and purpose of it all, even these things will manifest a loving Father in Heaven."
-- President Boyd K. Packer, "The Play and the Plan"