An apostolic letter on the Christian meaning of human suffering, given on the World Day of the Sick during the Holy Year of the Redemption. Taking as its text Saint Paul's words about completing in his flesh what is lacking in the sufferings of Christ, it moves through the world of human suffering, the problem raised by suffering in the Book of Job, the Cross as the answer God gives not in words but in his Son, the sharing of the Christian in Christ's redemptive suffering, and the parable of the Good Samaritan as the summons to those who stand beside the one who suffers.