You haven't actually asked a question, but I will focus on the conflict between Pahom and the Devil and how it functions allegorically in this excellent short story. This story is allegorical in that it operates on two different levels: the literal and the symbolic. It is clear that the characters and the events can be understood both for what they are - the literal meaning - and for the abstract principles they represent, or the symbolic meaning.
Note how the Devil is introduced eavesdropping in on the squabble between the two sisters and how he hatches his plan:
"All right," thought the Devil. "We will have a tussle. I'll give you land enough. and by means of that land I will get you into my power."
Thus the "tussle" begins, with Pahom gaining ever more land yet finding that however large the amount, it is never enough. The story narrates to us how he treats others in the way that he was once treated as a landless serf and finally how, overcome by his own greed to gain land, Pahom dies, answering the question in the title, showing that in the end, he only needed enough to bury himself in. It is clear therefore that the Devil symbolically represents human weakness and in particular greed, and based on this interpretation, Pahom may represent the human soul, who is lead astray by weakness. Thus the message of the story is made clear: unchecked ambition and greed destroy people. Striving too much for material gain leads to unhappiness, and eventually, a sad lonely death.