[And this brings me to] the other sense of glory—glory as brightness, splendour, luminosity. We are to shine as the sun, we are to be given the Morning Star. I think I begin to see what it means. In one way, of course, God has given us the Morning Star already: you can go and enjoy the gift on many fine mornings if you get up early enough. What more, you may ask, do we want? Ah, but we want so much more—something the books on aesthetics take little notice of. But the poets and the mythologies know all about it. We do not want merely to see beauty, though, God knows, even that is bounty enough. We want something else which can hardly be put into words—to be united with the beauty we see, to pass into it, to receive it into ourselves, to bathe in it, to become part of it. That is why we have peopled air and earth and water with gods and goddesses and nymphs and elves—that, though we cannot, yet these projections can enjoy in themselves that beauty, grace, and power of which Nature is the image. That is why the poets tell us such lovely falsehoods. They talk as if the west wind could really sweep into a human soul; but it can’t. They tell us that ‘beauty born of murmuring sound’ will pass into a human face; but it won’t. Or not yet. For if we take the imagery of Scripture seriously, if we believe that God will one day give us the Morning Star and cause us to put on the splendour of the sun, then we may surmise that both the ancient myths and the modern poetry, so false as history, may be very near the truth as prophecy. At present we are on the outside of the world, the wrong side of the door. We discern the freshness and purity of morning, but they do not make us fresh and pure. We cannot mingle with the splendours we see. But all the leaves of the New Testament are rustling with the rumour that it will not always be so. Some day, God willing, we shall get in. When human souls have become as perfect in voluntary obedience as the inanimate creation is in its lifeless obedience, then they will put on its glory, or rather that greater glory of which Nature is only the first sketch.
The Weight of Glory by C.S. Lewis
In the section in bold type in the quote above we see the rule by which Lewis led his own life. He wrote somewhere (although I do not have time to find it right now) that he lived out his Christian faith according to what St. Paul wrote in his letter to the Philippians, “work out your own salvation with fear and trembling; for God is at work in you, both to will and to work for his good pleasure.”
The underlined phrases indicate the most important parts. First of all, God willing we, in the end, will arrive in Heaven. Of course, He does will that all those He has made in His own image should be with Him forever. But, from the teaching of our Lord Jesus Christ, we know that not everyone will achieve salvation. This is due to the fact that our salvation also requires our voluntary obedience. God does not force anyone to do anything against his own will. Therefore, we can choose to turn away from God – to reject Him and Heaven.
If we desire to be with Him in Heaven then we must cooperate with Him by being voluntarily obedient to the teachings of His Son, which are contained in their fullness in the Catholic Church.