Christian belief that Christ will come again to judge the living and the dead is ultimately an act of faith that our actions in life actually mean something. It is a way of saying first that we are free and responsible creatures who must make our way in the world by choosing the good. Second, it is a way of affirming that death is not an ending, but a transition. Third, it recognizes that the only one who can judge our actions as human beings must be greater than us. Fourth, it trusts that Christ, who walked among us, was God, and that his promises about life after death are as close an approximation of what awaits us as language can afford. Finally, this belief is an act of hope: for God calls Christians to acts of humility, of self-sacrifice, of suffering in love—in short, to eschew creature comforts for the sake of building the world he has in mind.
Belief that Christ judges the living and the dead is a way of saying that all these choices are, in the end, abundantly worthwhile.