Her point in this poem is that if only God would let her see the glorious soldier as the angel he has become in the afterlife then it will give her the courage to face death and not be afraid of dying since she would know that there is something awaiting her on the other side.
Yet there is no resolution in the poem, she does not see the soldier “In [his] epauletted white” (as in he’s been transformed into an angel in white robes), she is only asking “God” to let her “behold” the image because as it stands right now she doesn’t have the strength of faith to face the “foe” and fight the “fight”. She wants proof, but God remains silent all through the poem.
And this doubt is carried over from the previous poem, “When I count the seeds” which she describes as the “Bee” whose sting of doubt she is trying to avoid. That poem predicts the countless dead who will lay on the battlefields of the US Civil War which will occur in just a few years, and perhaps her doubt is a manifestation of the uncertainty of the times in which the future of the nation was in doubt. In other words, she wants to know that everything will work out and that fighting the battle to come will be worth it and won’t just result in a lot of people laying in graves, that our lives, like her nation, will live on.