as far as the "Glove story"
Thought this was a good theory from IMDB.
The context of the glove story was Lester incredulously telling Molly he's not a monster, so the tale clearly had something to do with how Molly perceives Lester, or at least how she perceives human evil and human kindness.
She's talking about doing something for other people, even when you don't have to. The whole time throughout the investigation, Lester was never as helpful as he could have been, he was always evasive and got in the way of the investigation. Even when they had Malvo's pictures in front of him and it was clear that Lester knew who he was - Lester refused to help them find him, or give them extra information, information that could have potentially helped save more lives. Linda died because Lester chose to do nothing to help her -as far as Molly knew, Lester knew Malvo was after him, yet he let his wife go alone to the shop wearing his coat. Even if he is not an active monster, his inaction and unwillingness to help makes him a passive one.
So the story is about the difference between action and inaction - the man on the train can either lose a glove, or he can give a pair of gloves away, and that makes a big difference to the outcome of the story, turning it from something negative (losing) into something positive (giving). Molly is saying that the difference between Lester's decision not to act (not helping the police, letting his wife go to the shop etc), and the decision of a person who had chosen to act in those circumstances, was one that made him a selfish, and passive, monster. That is even without her knowing the truth of what he did to his wife. Lester didn't get the point of the story at all - he can only see as far as himself (as the cabbage, fox and rabbit riddle shows later - he just has a logical mind suited to solving problems for himself alone).
I think the tale also ties in with Bill's actions by telling Molly she should be chief. Bill is a good person, the opposite of Lester. He can only see the good in others. A lesser (Lester!) man would have felt shown up by, and envious of, Molly for having been so against her theory the whole time and then being shown his error by the FBI's clear excitement at her 'excellent work'. If it were Lester in Bill's shoes, for example, he would have probably made Molly suffer for this to reassert himself, but Bill just recognises that he is not cut out for the job - if anything he is too compassionate and too quick to believe the best in people. So he bows out and offers her the job, very gracefully. He lost one glove (the whole Malvo/Lester case) and so he gives up the other (retires and gives Molly the position of Chief).