The answer it the thesis. It explains what the entire essay will be about in one sentence.
When a story is written in third person point of view, it may cut off some of the personal feelings you might get if you were reading the story in first person, or even second person point of view. The thing is, first person is a lot more personal than third person. Third person is kind of like just telling you the story. (Although it is not narrative)
In this excerpt, Edwards is attempting to convince people that they need to believe in and love the Holy God. You can infer from the text that they were not appreciative enough
It means that you could truly tell how upset the character was, and the true meaning wept over everyone, of how cruel the world is