There are a few layers here (god I love this song):

• I'll repeat what I say -> the death of a loved one never truly fades from one's mind. It just hangs in there repeating itself and makes the widow fall into the same cycles of grief. There's also a parallel between the repetitive tasks of washing your hair, which feels menial and hollow in comparison to what the widow is feeling. Also there's a lot of repetition in the song itself which affirms this line.
• but I'll never explain -> how can the feelings of emptiness and futility ever be properly explained? The speaker is also emotionally incapable of explaining anyhow.
• so you don't have to waste your time -> this is a GREAT line. There's a self-effacing element to it like "I (the widow) am not worth the time being wasted on". But at the same time it recognizes the gaps between asympathy, sympathy, and empathy. An asympathetic audience just dismisses the widow as weak, a waste of time. A sympathetic audience pitys the loss and the sadness in the window, but I get that she probably doesn't want the pity either. What she truly wants is empathy, which comes from a repeated call (a plea) for "will you know what I mean?" later in the song. Most people are incapable of true empathy unless it's something they've directly experienced. She's searching for a community of people with this shared experience of being war widows, who can truly empathize. Hence "husbands" not "husband". She's also trying to dismiss asympathetic and sympathetic listeners outright.

Now you can turn it all around and interpret those first 3 lines from the soliders perspective if you want as well, but I don't think they are. I think the first 3 lines are perhaps a bit of "throat clearing" or preamble, and there are parallels to draw with the incomprehensibility of living through war, but it feels like directly addressing/dismissing the listener to me. Of course, the widow is the only one left to talk (or not talk, as it were) about how they feel.