36 Like action, suffering is a part of our human existence. Suffering stems partly from our finitude, and partly from the mass of sin which has accumulated over the course of history, and continues to grow unabated today. Certainly we must do whatever we can to reduce suffering: to avoid as far as possible the suffering of the innocent; to soothe pain; to give assistance in overcoming mental suffering. These are obligations both in justice and in love, and they are included among the fundamental requirements of the Christian life and every truly human life. Great progress has been made in the battle against physical pain; yet the sufferings of the innocent and mental suffering have, if anything, increased in recent decades. Indeed, we must do all we can to overcome suffering, but to banish it from the world altogether is not in our power. This is simply because we are unable to shake off our finitude and because none of us is capable of eliminating the power of evil, of sin which, as we plainly see, is a constant source of suffering. Only God is able to do this: only a God who personally enters history by making himself man and suffering within history. We know that this God exists, and hence that this power to “take away the sin of the world” ( Jn 1:29) is present in the world. Through faith in the existence of this power, hope for the world's healing has emerged in history. It is, however, hope—not yet fulfilment; hope that gives us the courage to place ourselves on the side of good even in seemingly hopeless situations, aware that, as far as the external course of history is concerned, the power of sin will continue to be a terrible presence.
Source: Spe Salvi (Vatican.va)