Eyeglass lenses serve the purpose of bending (refracting) light in such a way as to make things more clearly perceptible to us. Without going into more detail than would be interesting, I will tell you that there are different kinds of eyeglass lenses, but they can be broken down into two categories (if we’re talking in the plainest terms).
These two categories are simple (spherical) and compound (toric). The spherical lens is basically one consistent curve throughout the body of the lens. It is used to correct simple, though even severe, nearsightedness and farsightedness (myopia and hyperopia, respectively). The compound lens has a cylindrical dimension in addition to the spherical element. This means that there is an additional curve in the lens which is designed to refract light not only in a straight-on way, but also in an angular way. The angle or axis of the cylindrical cut is important, but this is a blog post of an analogy, not a book on optical theology.
Now, of course this information does not qualify you to be an optician, and the analogy, like any good analogy, breaks down if taken further than intended, but we can look at the Bible as our lens. It enables us to see what we are incapable of seeing without aid, namely, God. And it is not merely a simple spherical lens that we need. We need a compound lens because we are not simply myopic, we are also astigmatic.
The analogy needs work, so you are free to enhance it! In the mean time, he who has eyes to see…let him see.