63 And the blessed Apostle Paul, writing to the Thessalonians, says: “Now we beseech you, brethren, concerning the coming of our Lord Jesus Christ, and our gathering together at it, that you be not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letters as from us, as that the day of the Lord is at hand. Let no man deceive you by any means; for (that day shall not come) except there come the falling away first, and that man of sin be revealed, the son of perdition, who opposes and exalts himself above all that is called God, or that is worshipped: so that he sits in the temple of God, showing himself that he is God.
Do you not remember that when I was yet with you, I told you these things? And now you know what withholds, that he might be revealed in his time. For the mystery of iniquity does already work; only he who now lets (will let), until he be taken out of the way. And then shall that wicked be revealed, whom the Lord Jesus shall consume with the Spirit of His mouth, and shall destroy with the brightness of His coming: (even him) whose coming is after the working of Satan, with all power, and signs, and lying wonders, and with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth.
And for this cause God shall send them strong delusion, that they should believe a lie: that they all might be damned who believed not the truth, but had pleasure in unrighteousness.” And Esaias says, “Let the wicked be cut off, that he behold not the glory of the Lord.”
Source: The Antichrist (New Advent)