In "The Bet" by Anton Chekhov, what does the story tell us about life and human nature?
Please remember that you are only allowed to ask one question. Your original question contained several separate questions, therefore I have edited it down according to enotes regulations.
This story remains incredibly ambiguous in terms of its purpose and ending, and thus is open to multiple interpretations. For me, one of the themes that clearly comes out is that earthly rewards are of little worth when we consider the spiritual and eternal rewards that are open to us. This is clearly demonstrated in the letter that the lawyer leaves behind after he leaves his shelter, thus breaking the bet a few moments before winning it, showing his contempt for the terms of the bet and the money he was due to win. Note what he says:
"And I despise your books, I despise wisdom and the blessings of this world. It is all worthless, fleeting, illusory, and deceptive, like a mirage. You may be proud, wise, and fine, but death will wipe you off the face of the earth as though you were no more than mice burrowing under the floor, and your posterity, yoru hsitory, your immortal geniuses will burn or freeze together with the earthly globe."
The lawyer is astounded at those, who through pursuing earthly wisdom and possessions, "exchange heaven for earth." Thus one possible theme or message is very clearly the way that we have lost our focus on spiritual and eternal rewards and have instead exchanged those for earthly rewards such as materialism.