Adam Clarke on Matthew 3:12

Whose fan is in his hand - The Romans are here termed God's fan, as, in Mat 3:10, they were called his axe, and, in Mat 22:7, they are termed his troops or armies.

The winnowing fan of the Hindoos is square, made of split bamboo; and the corn is winnowed by waving the fan backwards with both hands - "Whose fan is in his hand."

His floor - Does not this mean the land of Judea, which had been long, as it were, the threshing-floor of the Lord? God says, he will now, by the winnowing fan (viz. the Romans) thoroughly cleanse this floor - the wheat, those who believe in the Lord Jesus, he will gather into his garner, either take to heaven from the evil to come, or put in a place of safety, as he did the Christians, by sending them to Pella, in Coelosyria, previously to the destruction of Jerusalem. But he will burn up the chaff - the disobedient and rebellions Jews, who would not come unto Christ, that they might have life.

Unquenchable fire - That cannot be extinguished by man.