Jesus’ threshing floor is the people of Israel. Just as grain is gathered into the barn while the chaff is burnt, so Christ will gather his subjects and condemn the godless to hell (see Matthew 13:30, Matthew 13:42, Matthew 13:50). Christ will separate his people who, figuratively, take refuge in his barn, by his Spirit.
The threshing floor refers to the people of Israel. Threshing traditionally took place on a hill. The grain was placed in a circle and treaded out either by oxen or donkeys (Deuteronomy 25:4, 1 Corinthians 9:9, 1 Timothy 5:18), or with threshing equipment. In order to separate the chaff and other rugged materials from the wheat, everything is thrown into the air with a winnowing fork (in this case a wooden fork or a shovel). The wind carries away the chaff while the grain falls back on the ground. Just like grain is gathered in a barn while the chaff is burnt, so the Messiah will gather the citizens of his kingdom and condemn the godless to eternal punishment (see Matthew 13:30, Matthew 13:42, Matthew 13:50).1
The Lord will come to the threshing floor (the people of Israel) and separate the chaff from the grain. That separation happens when he uses his winnowing fork. His coming is decisive, both as a safe haven against wrath and for the burning in wrath. The barn in which the grain is stored is another image used for the protection and guidance of the Holy Spirit. John shows most emphatically that the people of Abraham’s only hope of life lies in the grace offered in the coming of the Anointed One.2
12 His winnowing fork is in his hand, and he will clear his threshing floor and gather his wheat into the barn, but the chaff he will burn with unquenchable fire.”