"Do not weep." You'll hear that again and again in this poem because it's part of the refrain. But it's more than that, of course. Weeping is what people do when they lose somebody they love, so it's a little bizarre to tell somebody not to weep after they find out somebody has died. But it becomes clear soon after the poem's opening lines that the speaker is being ironic, or rather that he is exposing some bogus military cliché about the kindness of war. So weep away, maidens, mothers, and babes.
Line 1: The speaker tells a maiden not to weep because war is kind. This is an example of irony, as war is definitely not kind, thank you very much.
Line 4: The phrase "do not weep" is repeated again, making it a refrain.
Line 12: The refrain is repeated again, but this time, the speaker addresses a babe (i.e. a baby, not a hot chick).
Line 15: Yet again, the speaker tells his addressee "do not weep." We get it already, ya jerk.
Line 25: The speaker tells the mother not to weep because war is kind. This is the last time we hear the refrain, and we can't say we're sad about it. We've had enough weeping to last us a lifetime.