Christ the Lord already reigns through the Church, but all the things of this world are not yet subjected to him. The triumph of Christ’s kingdom will not come about without one last assault by the powers of evil.
On Judgment Day at the end of the world, Christ will come in glory to achieve the definitive triumph of good over evil which, like the wheat and the tares, have grown up together in the course of history.
When he comes at the end of time to judge the living and the dead, the glorious Christ will reveal the secret disposition of hearts and will render to each man according to his works, and according to his acceptance or refusal of grace.
–Catechism of the Roman Catholic Church, paragraphs 680-682