John Chrysostom

"Then shall many be offended, and shall betray one another, and many false Christs and false prophets shall arise, and shall deceive many." This is the greater evil, when the war is intestine too, for there were many false brethren. Seest thou the war to be threefold? from the deceivers, from the enemies, from the false brethren. …

Homily on the Gospel of Matthew 75 ↗

Thomas Aquinas

And then shall many be scandalized. Here he sets forth the dangers from those within. For there is a threefold scandal that you will suffer: namely, that of the weak, mutual injury, and debility. Hence he says, then shall many be scandalized; because even the very perfect will be scandalized; hence above, 18:7: It must needs be that scandals come. Hence even the elect are troubled when they see scandals; hence Paul was saying, 2 Corinthians 11:29: Who is scandalized, and I am not on fire? And they shall betray one another. …

Commentary on Matthew ↗

Remigius of Rheims

But the whole passage might be referred to the end of the world. For then shall many be offended, and depart from the faith, when they see the numbers and wealth of the wicked, and the miracles of Antichrist, and they shall persecute their brethren; and Antichrist shall send false Prophets, who shall deceive many; iniquity shall abound, because the number of the wicked shall be increased; and love shall wax cold, because the number of the good shall diminish.

Catena Aurea by Aquinas ↗