Albert Barnes Commentary Matthew 3:12

"whose fan is in his hand, and he will thoroughly cleanse his threshing-floor; and he will gather his wheat into the garner, but the chaff he will burn up with unquenchable fire." — Matthew 3:12 (ASV)

His fan. It seems probable that this was some portable instrument, made light, so that it might be easily carried about. The fan is a well-known agricultural instrument that was used by the Jews, as it is today, to separate grain from the chaff. The usual custom was to throw the grain in the air with a large shovel and allow the wind to drive the chaff away, but it is probable that the fan was often used .

His floor. The threshing-floor was an open space, or area, in the field, usually on an elevated part of the land (Genesis 1:10). It had no covering or walls. It was a space of ground thirty or forty paces in diameter, made smooth by rolling it or treading it hard. A high place was selected for the purpose of keeping it dry and for the convenience of winnowing the grain by the wind.

The grain was usually trodden out by oxen. Sometimes it was beaten with flails, as with us, and sometimes with a sharp threshing instrument made to roll over the grain and cut the straw at the same time (Isaiah 41:15). After being threshed, it was winnowed. The grain was then separated from the dirt and coarse chaff by a sieve, and then further cleansed by a fan, an instrument to produce an artificial wind. This method is still practiced in eastern nations.

Shall purge. To cleanse or purify; to remove the chaff, etc.

The garner. The granary or place to deposit the wheat.

Unquenchable fire. This refers to fire that shall not be extinguished, that will utterly consume it. Here, the floor represents the Jewish people. The wheat represents the righteous, or the people of God. The chaff represents the wicked. They are often described as being driven away like chaff before the wind (Job 21:18; Psalms 1:4; Isaiah 17:13; Hosea 13:13).

They are also represented as chaff that the fire consumes (Isaiah 5:24). This image is often used to express judgments. Isaiah 41:15 says, Thou shalt thresh the mountains, and beat them small, and shalt make the hills as chaff. By the unquenchable fire is meant the eternal suffering of the wicked in hell (2 Thessalonians 1:8–9; Mark 9:48; Matthew 25:41).