I'm going to unpack this beautiful quote from C.S. Lewis in a rather unusual way, not because I have to but because I choose to. If the human mind (ever-insistent on being its own place) can make a heaven of a hell or hell of heaven, the orientation of the soul will dictate its reaction to heavenly things and hellish things respectively. Creatures bearing the Image of God and with that Image broken by the sin of Adam, will either move toward light or darkness in the spiritual realms. This is because of instinct. Depending on the conditioning they undergo in life, souls will either scatter from the presence of light like cockroaches in a dark room or run toward it like adoring children into the embrace of a long-absent parent. This has to do with the Presence of God being either the best thing there is or the worst, depending on who it is being drawn into that Presence. Room 777 is the place where there is no darkness. This, because there is no darkness in Him who meets each of us there, privately. All that is done in the dark will be brought to the light, to the very person of Light.
In George Orwell's novel 1984, there was "no darkness" inside the dreaded Room 101 only because the electric lights never went out. It was a place of torment for whomever was a prisoner there, and even for those Oceania citizens who anticipated being brought there. During his ordeal in Room 101, Winston heard a voice in his ear utter the words: "Don't worry, Winston; you are in my keeping. For seven years I have watched over you. Now the turning-point has come. I shall save you, I shall make you perfect." At the time, Winston wasn't sure if he was sleeping, awake, or in a drug-induced delirium. The blackshirts and the Party intellectuals had worked him over so badly that he no longer knew where he was, who he was, why he was. Was it O'Brien that had spoken those words to him? He wasn't sure. What he knew for certain was that it was the same voice he'd heard in a dream seven years prior to his capture and incarceration in the Ministry of Love. Was it the voice of O'Brien all along, or was this the in-universe equivalent of theodicy? If God did exist in the world of 1984, Big Brother certainly was that God. The still small voice in Winston's ear might have been that of Big Brother, comforting Winston in his darkest hour. The essence of Winston's thoughtcrime was his rebellion against The Party but ultimately against its enigmatic leader, the stern face whose eyes saw everything. In the secret place of his heart, in the crucible of Room 101, Winston Smith gave up his struggle and gave in to Big Brother. At long last, Winston allowed himself to be immolated and reborn as a child of the All-Beneficent Mustachioed One.