Greek Expositor (anonymous) — as excerpted in the Catena Aurea on Luke 3:15-17

“(ubi sup.) By these words then, He shall baptize with the Holy Spirit, He signifies the abundance of His grace, the plenteousness of His mercy; but lest any should suppose that while to bestow abundantly is both in the power and will of the Creator, He will have no occasion to punish the disobedient, he adds, whose fan is in his hand, shewing that He is not only the rewarder of the righteous, but the avenger of them that speak lies. But the fan expresses the promptitude of His judgment. For not with the process of passing sentence on trial, but in an instant and without any interval he separates those that are to be condemned from the company of those that are to be saved.”