This metaphor compares how the Christ will separate the righteous people from the unrighteous people to how a man separates wheat grain from chaff. It can be translated as a simile to make the connection more clear: "The Christ is like a man whose winnowing fork is in his hand."(See: [[rc://en/ta/man/translate/figs-metaphor]], [[rc://en/ta/man/translate/figs-simile]])
This is a tool for tossing wheat up 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. (See: [[rc://en/ta/man/translate/figs-metaphor]])