Theophylact of Ohrid

He did not say: that they may receive punishment (for even if the antichrist had not come, the unbelievers would have had to be punished); but he says: that they may be condemned, so that they would be without excuse. Will they say that the reason we did not believe in Christ was that His disciples proclaimed Him as God, while we heard that there is one God, from Whom are all things? In that case, how did you believe the antichrist, who passes himself off as god? …

Commentary on 2 Thessalonians ↗

Ambrose of Milan

Who, then, is the Lord Who makes us to increase and abound before God and our Father at the coming of the Lord Jesus? He has named the Father and has named the Son; Whom, then, has he joined with the Father and the Son except the Spirit? Who is the Lord Who establishes our hearts in holiness. For holiness is a grace of the Spirit, as, too, is said farther on: "In holiness of the Spirit and belief of the truth."

On the Holy Spirit, Book 3, Chapter 14, 95 ↗

Thomas Aquinas

But the punishment only is eternal damnation; hence he adds "that all may be judged", namely with the judgment of condemnation. "And those who have done wickedly shall go forth to the resurrection of judgment" (John 5:29). "Who have not believed the truth." "He who does not believe is already judged" (John 3:18).

Commentary on 2 Thessalonians ↗