If it is a work that a man has determined he wills to do by his will, why would he have fear and trembling?
As I remember the story of Jonah, God had ordained a work for him and he sure had fear and trembling
We fear because we have a responsibility to work toward God and not away from Him. Since it is our choice, and we are not omniscient, we fear to err.
But if God works through us like a gardener works through a spade, then we would not have to fear anything. A tool has no reason to fear.