This poem is about a mother who gets the feeling that her son has died in the war long before she receives word of it by telephone, telegram, or in person. It's about her trying to deny hearing the truth and trying to live in her own world where her child is still alive. Her daughter comes into the son's room and sees her cleaning the place as if there's still a need for it to be cleaned, a need to appease the one that lives there.
I feel bad for the mother. I haven't experienced anything like this myself, and I hope it will be a while before I do, but to have someone dear to you die definitely seems like it would be a heartbreaking experience.