What does the farmer and woodman represent in A Tale of Two Cities?

The Woodman, who -is- Fate, is said to have marked trees to be cut down and be chopped into boards. These trees, then, are about to be transformed into the frame for the blade of the guillotine. In other Words, Fate is designing that instrument of death called the guillotine.

The Farmer, who -is- Death, has set apart typical farmer's carts, called tumbrils (a cart to carry dung), to be the vehicles in which the doomed were lead to their fate...the guillotine. In other Words, Death (the farmer...or, the reaper) has chosen the vehicles of transportation, to carry the people marked for it, to that execution.

Fate and Death were working through the injustices occurring in France against the peasants. They were working quietly towards the goal of death and destruction, which culminated in The French Revolution. None of the aristocracy saw the handwriting on the wall; they missed the telltale signs of what was about to explode and envelope them all. The Woodman (fate) and the Farmer (death) are symbolic of the coming destruction of the aristocracy and any deemed enemies of the Revolution (this period was called The Reign of Terror).