John Chrysostom — as excerpted in the Catena Aurea on Matthew 24:9-14

“Having named two sources of opposition, that from seducers, and that from enemies, He adds a third, that from false brethren; And then shall many be offended, and shall betray one another, and shall hate one another. See Paul bewailing these same things, Without were fightings, within were fears; (2 Cor. 7:5. 2 Cor. 11:26. v. 13.) and in another place; In perils among false brethren, of whom he says, Such are false Apostles, deceitful workers.”