Rabbi Harold Kushner explained in his foreword to Man’s Search for Meaning:
The greatest task for any person is to find meaning in his or her life. Frankl saw three possible sources for meaning: in work (doing something significant), in love (caring for another person), and in courage during difficult times. Suffering in and of itself is meaningless; we give our suffering meaning by the way in which we respond to it. . . .
Forces beyond your control can take away everything you possess except one thing, your freedom to choose how you will respond to the situation. You cannot control what happens to you in life, but you can always control what you will feel and do about what happens to you.
.. June 15, 1941: For a moment yesterday I thought I couldn’t go on living, that I needed help. Life and suffering had lost their meaning for me; I felt I was about to collapse under a tremendous weight. . . . I said that I confronted the “suffering of mankind” . . . but that was not really what it was. Rather I feel like a small battlefield, in which the problems, or some of the problems, of our time are being fought out. All one can hope to do is to keep oneself humbly available, to allow oneself to be a battlefield. 
This is what it means to hold the contradictions and the pain of the world, as we do in contemplation. Hillesum accepted her destiny. She believed, as I do, that we are called to be both the agony and the ecstasy of God—for the life of the world. For me, to be a Christian means to accept that battlefield, to accept and to somehow participate in the mystery of death and resurrection in oneself and in the universe. It is a process of “oneing” with Foundational Reality, which some call at-one-ment.
Social psychologist Diarmuid O’Murchu writes:
Creation cannot survive, and less so thrive, without its dark side. There is a quality of destruction, decay, and death that is essential to creation’s flourishing. . . . And the consequence of this destructive dimension is what we call evil, pain, and suffering. Obviously, I am not suggesting fatalistic acquiescence. Indeed, I am arguing for the very opposite: an enduring sense of hope, which it seems to me is not possible without first coming to terms with . . . the great paradox. It is . . . the unfolding cycle of birth-death-rebirth. And it transpires all over creation, on the macro and micro scales alike. 
Yes, I know, sisters and brothers, suffering is and will always be a mystery, maybe the major mystery.