Matthew 3:12. “Whose fan is in His hand, and He will thoroughly purge His floor, and gather His wheat into the garner; but He will burn up the chaff with unquenchable fire.”
This is actually a continuation of John’s description of the Lord in verse 12, Whose shoes, he said,he was unworthy to carry. To better understand this verse, we need to do a little bit of history.
In the Old Testament, a threshing fan was a wooden shovel or screen. The harvester would pick up a load of wheat and toss it into the wind in order for the lighter chaff, which was useless, to be blown away. The chaff would then be swept up and burned, while the good grain settled into a pile. This process was winnowing the wheat.
The winnowing process took place on a threshing floor. It was a space that had been hardened by the years of use from the worker’s feet, often using oxen to pull a winnowing sled across the floor; it was the place of both blessing and judgment. To purge the floor was to completely cleanse the wheat from all chaff, weeds, and other unclean materials. Often the wheat was pounded to separate the useful kernels from the waste, picturing God’s judgment in separating true believers from the dross of Christendom that claims the name of Jesus but does not truly know Him.
The threshing floor was a place of blessing because it was the place of harvest, where the crops would be cleansed for use in the coming year. The harvest time was a time of great rejoicing. At the end of the harvest, when all the good wheat had been separated and stored, the chaff would be swept together and burned, picturing the everlasting judgment to fall on those who do not receive Jesus as Messiah, as Savior.
So John uses an agricultural event that was familiar to all the Israelites to portray both the imminent coming of Jesus into His public ministry, and the far future final judgment of the end times, when God will separate the wheat (true believers) from the chaff (those who have a form of religion, but not the power).