There are few people whom I really love, and still fewer of whom I think well. The more I see of the world, the more am I dissatisfied with it; and every day confirms my belief of the inconsistency of all human characters, and of the little dependence that can be placed on the appearance of merit or sense.

This quote is basically saying that there are very few people whom the speaker really loves, and even fewer people of whom the speaker thinks well. Moreover, the more the speaker sees of the world, the more dissatisfied they become with it, and this further reinforces the idea that human characters are often inconsistent and it is difficult to rely on someone’s outward appearance of merit or sense.