In "Home Burial," name three things the wife is upset about. Which will be the hardest for her husband to address?

I think the three things the wife is upset about is, of course, the death of her child, her husbands seeming callousness towards the catastrophe, or, at least his inability to express his grief about it, and finally, the utter final loneliness and finality of death itself.

The husband tries, albeit unsuccessfully, to address the first two of his wife's concerns.  He tries to console her in her grief, saying, "Let me into your grief", even while he admits, "My words are nearly always an offence, I don't know how to speak of anything so as to please you.  But I might be taught".  Although he is unable to reach her, he is able to at least address the issues, and makes an attempt to understand.

The last of his wife's complaints is something the husband cannot do anything about, because it concerns the very nature of humankind.  The wife laments, "from the time when one is sick to death, one is alone, and he dies more alone...the world's evil".  She is expressing the sense that true communication is impossible ("You couldn't care!), and that man is doomed to live life in isolation, a condition that only becomes worse after death.