Here's how Baxter describes the two types of men. The first type are those who failed to appreciate the importance of books due to their parents' negligence when they were young.
The second type are the scholars who know how words work. They are what we call today "men with high breeding." Unfortunately, these men are clueless as to the nature, truth, and goodness of the things they speak.
Baxter asked the first type of men about the utility of their lives, time, and reason. Do they possess them just for the sake of the temporal things in this world? Or do they serve a higher purpose, which is to prepare for the afterlife?
I think the admonition about the character of the gospel as light is also applicable to the second type of men. He made analogies that men don't buy or trade in the dark or do their daily work in the dark. Cheating too is done in the dark, as are all the evil works of men. And that is why we need light, for it makes us safe and comfortable, and this is exactly the work of saving grace. Grace turns men from darkness to light and exposes the works of darkness.