On Perelandra, all the landmasses are islands, with the exception of a mountainous continent known as the Fixed Land, which Maleldil has forbidden the King and Queen to sleep or dwell on. Thus, throughout the story, the Fixed Land symbolizes the law of Maleldil. Weston (or the satanic being that inhabits his body) tries to erode the Green Lady’s trust in Maleldil by attacking the seeming illogic of this specific law (and hence all his commands, and the character of Maleldil himself). Ultimately, the Lady resists the temptation to disobey Maleldil’s command, realizing that she only desired to live on the Fixed Land because it was fixed—its stationery nature suggesting the desire to secure one’s own future rather than trusting in the waves Maleldil sends, each as it comes.
The Fixed Land Quotes in Perelandra
"I have said already that we are forbidden to dwell on the Fixed Land. Why do you not either talk of something else or stop talking?”
"Because this forbidding is such a strange one,” said [Weston’s] voice. "And so unlike the ways of Maleldil in my world. And He has not forbidden you to think about dwelling on the Fixed Land. […] [I]n our world we do it all the time. We put words together to mean things that have never happened and places that never were: beautiful words, well put together. And then tell them to one another. We call it stories or poetry. […] It is for mirth and wonder and wisdom.”
"What is the wisdom in it?"
"Because the world is made up not only of what is but of what might be. Maleldil knows both and wants us to know both.”