Over and over again in Anna Karenina, Tolstoy expresses his suspicion of man-made stuff. It seems that he thinks trains are ruining the Russian countryside by bringing peasants to the cities. Education destroys kids' natural instincts, contributing to dishonesty and (in the case of peasants) lack of ability. What all of this amounts to is that anything that Tolstoy perceives as interfering with an individual's relationship to nature (and that's both the individual's own human nature and nature, as in, the place where agriculture happens) is bad. Doing "good" means doing what you're born to do: in the case of peasants, Tolstoy wants them to stay in the country and farm as they were "meant to do." In the case of women, that means giving birth and being the heart of a husband's home. (Check out the theme of "Gender" for more on this topic.)
It is Levin's strong associations with the natural world (farming, walking, hunting) that allow him to find the meaning of life; his life in Moscow only confuses and tempts him to bad ways.
Levin's final epiphany tells us that individuals are "good" when they listen to their essential human natures; we find examples of this kind of goodness in Kitty's treatment of Nicholas and in the wealthy old peasant's development of his agricultural life in Part 3, Chapter 25.