Like you, I'm always on the lookout for good books for seekers. You know who seekers are, right? These are the folks who come to your church NOT because they occasionally like to feel less guilty by attending, but because they are actually looking for answers. These are the folks who want to sit down and ask you questions about life, suffering, truth, the Bible, or where is God in all this mess, and seem to genuinely want answers. So...
What are your Big 5 books for seekers?
These will likely be books on the gospel or apologetics. You should try to stick to books that are meant for seekers or books that unintentionally just work very well with seekers. As best you can, stick with general books for seekers and not books on one issue only. If one really stands out to you, that's cool, but I would prefer lists that will help us all with good books for seekers in general. And please don't mention Scripture. We get it, the Bible is good for seekers. :)
