38 He promised also to the Apostles the participation in this His glory. So shall it be in the end of the world. The Son of Man shall send forth His angels, and they shall gather together out of His Kingdom all things that cause stumbling, and them that do iniquity, and He shall send them into the furnace of fire: there shall be the weeping and gnashing of teeth. Then shall the righteous shine forth as the sun in the Kingdom of their Father. He that has ears to hear, let him hear. Were their natural and bodily ears closed to the hearing of the words, that the Lord should need to admonish them to hear?
Yet the Lord, hinting at the knowledge of the Mystery, commands them to listen to the doctrine of the faith. In the end of the world all things that cause stumbling shall be removed from His Kingdom. We see the Lord then reigning in the splendour of His body, until the things that cause stumbling are removed. And we see ourselves, in consequence, conformed to the glory of His body in the Kingdom of the Father, shining as with the splendour of the sun, the splendour in which He showed the fashion of His Kingdom to the Apostles, when He was transfigured on the mountain.
Source: On the Trinity (New Advent)