"How Much Land Does a Man Need" is a parable, which is a story that parallels some event(s) with a moral lesson. Pahom's wife had been correct in that, although poor, they had everything they needed. However, overhearing this, Pahom concludes that if he had more land he would not fear even the Devil himself. Therefore, Pahom has made the decision that land and/or wealth would make him so prosperous and powerful that he would be beyond the Devil's influence. However, that influence presents itself each time Pahom longs for more land.
Prior to the sisters' discussion, Pahom already had as much land as he needed to be happy. He let greed overtake that contentment and it ruined him. The other significant aspect of the title is that each man only really needs enough land to be buried in.
His servant picked up the spade and dug a grave long enough for Pahom to lie in, and buried him in it. Six feet from his head to his heels was all he needed.
The moral is that there is no specific amount of land or wealth required to make a person happy. Companionship is clearly a much better indicator of happiness but Pahom does not even consider his wife when he goes to such lengths to acquire more land. This story is an example of dramatic irony; this is when the audience is aware of some truth (that greed will be Pahom's downfall) that the character (Pahom) is unaware of. The ironic ending, or the brutal truth, is that the answer to the question, "How Much Land Does a Man Need," is "six feet from his head to his heels."