Question

Can anyone please help with understanding this poem?

Shiloh: A Requiem (April, 1862)
BY HERMAN MELVILLE
Skimming lightly, wheeling still,
The swallows fly low
Over the field in clouded days,
The forest-field of Shiloh—
Over the field where April rain
Solaced the parched ones stretched in pain
Through the pause of night
That followed the Sunday fight
Around the church of Shiloh—
The church so lone, the log-built one,
That echoed to many a parting groan
And natural prayer
Of dying foemen mingled there—
Foemen at morn, but friends at eve—