On demons
I believe [in the existence of the devil] not in the sense that it is part of my creed, but in the sense that it is one of my opinions. My religion would not be in ruins if this opinion were shown to be false. Till that happens—and proofs of a negative are hard to come by—I shall retain it. It seems to me to explain a good many facts. It agrees with the plain sense of Scripture, the tradition of Christendom, and the beliefs of most men at most times. And it conflicts with nothing that any of the sciences has shown to be true.
Frankly, I’m disappointed that CS Lewis appears to offer such a weak affirmation for the source of all evil which is Satan. If the God of the Bible exists, then so does Satan, which the Bible also affirms. Likewise, the demons were revealed by Jesus Christ who would cast them out from possessed persons. These are the fallen angels whom lucifer corrupted and were cast out of heaven along with him.
If there were no Satan and his followers, including men, continuously stirring up evil on this earth, there would be peace.
Yes, rather weak, but then Lewis was still in process of shedding his atheism and affirmation of evolution. It’s in the second book of his Narnian Chronicles that we read his full orbed belief in creation ex nihilo.