Origen
Catena Aurea · Lukasevangelium 3
And as the people were in expectation, and all men mused in their hearts of John, whether he were the Christ, or not; John answered, saying unto them all, I indeed baptize you with water; but one mightier than I cometh, the latchet of whose shoes I am not worthy to unloose: he shall baptize you with the Holy Ghost and with fire. Whose fan is in his hand, and he will throughly purge his floor, and will gather the wheat into his garner; but the chaff he will burn with fire unquenchable.
Or, because without the wind the wheat and chaff cannot be separated, therefore He has the fan in His hand, which shews some to be chaff, some wheat; for when you were as the light chaff; (i. e. unbelieving,) temptation shewed you to be what you knew not; but when you shall bravely endure temptation, the temptation will not make you faithful and enduring, but it will bring to light the virtue which was hid in you.