Life
Life is a major theme of Perelandra: it's evident in the plot, the environment, and everywhere else. Perelandra is essentially another Garden of Eden. It's beautiful, vibrant, and perfect, unblemished by sin - the way life is supposed to be. In that way, it's an ultimate realization of Life. Ransom's mission is to save the inhabitants from the foul interference of the Tempter, the fruit of whom leads to death, so his mission is the preservation of Life as well. The beauty of the Perelandran ecosystem is equally striking; life seems to pervade the entire planet, pure and undiluted. The result of all of these elements is that Perelandra is the installment of the Space Trilogy most concerned with Life.
Temptation
In opposition to Ransom's mission of Life, the "black archon" (Satan) is at work seeking to "steal, kill, and destroy" (John 10:10). The evil eldila at the beginning assail Lewis's mind with doubt, attempting to make him turn back from his journey and disbelieve Ransom's account. Weston also serves as a figure of temptation: it becomes clear that Satan has inhabited him as he did the serpent in the Garden of Eden, planting doubt and desire into the innocent mind of Tinidril (Perelandra's Eve), tempting her to sin.
Universal Truth
The claims to Truth expressed in Perelandra are quite literally universal. The message of Maleldil's sacrifice for humanity at the behest of the Old One is applicable to all rational beings from all planets in the Field of Arbol (Solar System). This universality is evident even in the language. The language Ransom learned on Malacandra (Hressa-Hlab, also known as Old Solar and Hlab-Eribole-Cordi) was at one point spoken on all inhabited planets, and was spoken on Earth in the Garden of Eden before the Fall. Now Earth lies in darkness, but the truth brought by Maleldil is accepted by all the other sentient beings in the universe.
God's Use of Ordinary People
Lewis asks why the Oyarsa has asked Ransom, of all people, to go on this mission to save Perelandra. He is, after all, just a weak, mortal human being with no particular talents save that of language. Ransom responds by saying that that is the mysterious and wonderful ways of God; he uses ordinary people (Moses, Gideon, Isaiah, etc.) to accomplish great things for His ultimate glory. Ransom himself is woefully inadequate, as he realizes in conversation with the beautiful and innocent Tinidril on the Venusian paradise, but he accomplishes his purpose, banishing Sin from Perelandra and ensuring its continued harmony with Maleldil.
