As to why we should not read spiritual books I am at a loss. Most of these people will admit to reading fiction. Let's face it. These days when we read novels or watch television, even when we are very careful what we read or watch, we have to overlook some things. I have gotten pretty good at reading past words I would never say myself. In fact, I did not realize that was what I was doing until I began to listen to audio books. I received shock after shock when those words I automatically elided were suddenly spoken aloud in my ear! Now if we make allowances in some way for things like that, why can't we do the same for a good book on a helpful spiritual topic that just might have a line or two that we recognize as false doctrine? I assume that these oh-so-particular Christians do know their Bible well enough to recognize these things and not lose their faith. If not, why not?
We have historical documents telling us that Christians as far back as the late first and early second centuries read books on spiritual topics that are not included in the Bible. Why? For edification when the book was correct, and to find out what exactly people were teaching when they weren't. There is mention in the New Testament of other epistles, one written by Paul himself, that were not considered "scripture" and so are not included in the Bible. As far as reading things by people who were not Christians, we know Paul read pagan writers and quoted or alluded to them (Acts 17:28, Aratus in Phaenomena 5; Titus 1:12,13, Epimenides in de Oraculis; 1 Cor 15:33, Menander in Thais 218). Other books are mentioned in the Old Testament as well (Josh 10:13; 1 Chron 29:29, etc.). All of God's people through history have been readers.
So I keep some sort of spiritual book on hand to read in every day. No, it is usually not a fast, fun read, but I find I can give it 20-30 minutes easily. Sometimes I read a whole chapter, other times a section of a chapter. It depends on the book. Besides giving me information I would not have had any other way, they also prod me to pick up my Bible even more than I already do.
If you have missed them, check the right sidebar and click on "book reviews." I hope they will help you get started in what I believe is a worthwhile experience.
When you come, bring the cloak that I left with Carpus at Troas, also the books, and above all the parchments (2Tim 4:13)