"He is holding a winnowing fork because he is ready." John speaks of the Christ coming to judge people as if he were a farmer who is ready to separate wheat grain from chaff. Alternate translation: "He is ready to judge people like a farmer who is ready" (See: [[rc://en/ta/man/translate/figs-metaphor]])
This is a tool for tossing wheat into the air to separate the wheat grain from the chaff. The heavier grain falls back down and the unwanted chaff is blown away by the wind. It is similar to a pitchfork.
The threshing floor was the place where wheat was stacked in preparation for threshing. To "clear off" the floor is to finish threshing the grain. Alternate translation: "to finish threshing his grain"