John Chrysostom

"For many shall come in my name, saying, I am Christ, and shall deceive many." For the war, saith He, shall be twofold that of the deceivers, and that of the enemies, but the former far more grievous, as coming upon them in the confusion and turmoils, and when men were terrified and troubled. For indeed great was the storm then, when the Roman power was beginning to flourish, and cities were taken, and camps and weapons were set in motion, and many were readily believed.

Homily on the Gospel of Matthew 75 ↗

Jerome

For many will come in my name, saying: I am the Christ, and they will deceive many. One of them is Simon the Samaritan, whom we read about in the Acts of the Apostles, who claimed to be a great power of God (Acts 8). Leaving these things aside, he also wrote among other things in his own volumes: I am the word of God, I am beautiful, I am the Paraclete, I am omnipotent, I am all things of God. …

Commentary on Matthew ↗

Thomas Aquinas

Many will come in my name, saying: I am Christ. Someone comes as sent by Christ; so the disciples came. But others are said to come in the name of Christ who say they are Christ, usurping for themselves a name that is not given to another; Philippians 2:9: He hath given him a name which is above all names. Hence many deceivers will come, who will come of themselves; but Christ did not come of himself, but from God; hence John 7:28: I am not come of myself. …

Commentary on Matthew ↗