Paul wrote II Thessalonians to correct a false impression held by the members of the church in Thessalonica. He did this by telling them what Christ had revealed to him regarding the "gathering together with Christ" of those dead in Christ and those remaining alive when He returned. He opens by foretelling, first of all, that Christ's return will be preceded by a period of apostasy that could include anything from a falling away, a departure from doctrine or teaching, all the way to and including an outright political rebellion.
The second sign would be the appearance of the man of sin. This person has four different names or titles, but all of them are described similarly: the man of sin (II Thessalonians 2:3-10), the little horn (Daniel 7:8), the two-horned lamb who spoke like a dragon (Revelation 13:11-18), and the false prophet (Revelation 19:20). The description in each location is not exactly alike, but each adds to what the other gives. Consider this summary of comparisons.
In each case, the person described appears at the time of the end. This is the one piece of information that every one of them has in common.
In three of the four, his end—his destruction or annihilation—comes at the return of Jesus Christ (Daniel 7:8-9; II Thessalonians 2:3; Revelation 19:20).
In three of the four, it directly states or strongly implies the person speaks with great pompous words (Daniel 7:8-9; II Thessalonians 2:4; Revelation 13:11-14).
In three of the four, it directly states the person does miraculous, supernatural signs (II Thessalonians 2:9; Revelation 13:13-15; Revelation 19:20).
In two of them, the signs are done in the presence of the Beast, showing they are not the same figure (Revelation 13:13-15; 19:20).
In two of them, he deceives and leads people into idolatry (II Thessalonians 2:4,9-10; Revelation 13:12,14).
In two of them, he either makes war against the saints or causes those who would not worship the beast to be put to death (Daniel 7:21; Revelation 13:15).
In two of them, he either thinks to change times and law—suggesting the law of God—or he sets himself in the Temple of God, proclaiming himself to be God. The implication is that he has the authority to do these things (Daniel 7:25; II Thessalonians 2:4).
In two of them, his period of greatest influence is three and a half years (Daniel 7:25; Revelation 13:5).
All of these scriptures are describing the same person. The Bible shows that this person—the man of sin—has a direct connection to a large political power and has a religious influence. It should be understood that we are dealing with a personage and with prophecies of global significance.
John W. Ritenbaugh
A Place of Safety? (Part 4)
Other Forerunner Commentary entries containing Daniel 7:21:
2 Thessalonians 2:3-10