Optimism hopes for the best without any guarantee of its arriving and is often no more than whistling in the dark. Christian hope, by contrast, is faith looking ahead to the fulfillment of the promises of God, as when the Anglican burial service inters the corpse ‘in sure and certain hope of the Resurrection to eternal life, through our Lord Jesus Christ.’ Optimism is a wish without warrant; Christian hope is a certainty, guaranteed by God himself. Optimism reflects ignorance as to whether good things will ever actually come. Christian hope expresses knowledge that every day of his life, and every moment beyond it, the believer can say with truth, on the basis of God’s own commitment, that the best is yet to come.
J.I. Packer