How does Adam Bede represent the attainment of a better understanding of life?

As a work of realism, Adam Bede purports to give us an accurate portrayal of people as they are. As the characters depicted in the story are more recognizably real and less idealized than in other novels, it becomes possible for the reader to gain a better understanding of life as it is actually lived in concrete situations.
Eliot wants us to accept the characters in the story—and by extension, the people we encounter in our own lives—warts and all, with all their faults and foibles. Few if any of the characters in the story are saints, and that's the whole point. They are real people; their faults are our faults, and by examining them, we gain not just a better understanding of life itself, but of ourselves and how we appear to other people.
Eliot's humanistic realism is so all-embracing that we're invited to feel empathy—if not sympathy—for someone like Hetty Sorrel, who abandons her new-born child to die in a field. Even if we can never condone Hetty's actions, we can at least understand where she's coming from. This is a testament, not just to Eliot's extraordinary skills as a story-teller, but also to her remarkable ability to put herself inside her characters' shoes.