Only a man harrowing clods
In a slow silent walk
With an old horse that stumbles and nods
Half asleep as they stalk.
Only thin smoke without flame
From the heaps of couch-grass;
Yet this will go onward the same
Though Dynasties pass.
Yonder a maid and her wight
Come whispering by:
War's annals will cloud into night
Ere their story die.

 The first stanza had a man and his old horse, the second a burning pile of weeds, and this third stanza has two humans – a maid (young woman) and her “wight” (young man) They are the corollary to the opening stanza. 
 The colon provides a break, a  caesura , in which the pace slows and the heavy moral lesson is propounded in the last two lines.
In Time of The Breaking of Nations