The first of these is Out of the Silent Planet (1938) in which the hero Dr Ransom is kidnapped and forced to go to Mars in a spaceship by the evil scientist Dr Weston and his accomplice, Devine. They intend giving Ransom to some Martian beings known as Sorns, whom they believe will sacrifice him. Weston is after gold on the planet and also intends wiping out the native beings and making it a human world from which he can conquer the rest of space. Humans and science are the rulers of the universe in his mind.
Ransom escapes on Mars, or Malacandra as it is called, and meets with and befriends the Hrossa, the Sorns and the Pfifltriggi, who are the races of beings that live on the planet as well finding out about the Eldila, who are like angels or other dimensional spirit beings. All the life forms on Mars look to a leading eldil known as Oyarsa and above him there is a being called Maleldil, who is the equivalent of God.
Ransom learns that all the beings that live on Mars live in harmony presided over by Oyarsa, and that Earth is known as Thulcandra, the Silent Planet, which is ruled by a "Bent Eldil," who is clearly representing the Devil.
Space, as such, is full of life and the domain of the eldila and Earth has become a planet that is the odd one out in the solar system because of its "bent" ruler. Wikipedia describes the situation as follows:
"Because the eldila, who fill space (or "the heavens," which are depicted as warm and bright under the influence of the Sun) know nothing about what goes on inside those boundaries, Earth is called Thulcandra, "the silent planet". While Earth has fallen into evil, Mars has not. This represented one of Lewis's concerns about space travel: that fallen humanity would have nothing to offer other life in space other than our depravity."