Matthew Henry Commentary 2 Thessalonians 2:1-4

"Now we beseech you, brethren, touching the coming of our Lord Jesus Christ, and our gathering together unto him; to the end that ye be not quickly shaken from your mind, nor yet be troubled, either by spirit, or by word, or by epistle as from us, as that the day of the Lord is just at hand; let no man beguile you in any wise: for [it will not be,] except the falling away come first, and the man of sin be revealed, the son of perdition, he that opposeth and exalteth himself against all that is called God or that is worshipped; so that he sitteth in the temple of God, setting himself forth as God." — 2 Thessalonians 2:1-4 (ASV)

If errors arise among Christians, we should set them right; and good people will be careful to suppress errors that arise from mistaking their words and actions. We have a cunning adversary, who watches to do mischief and will promote errors, even by the words of Scripture. Whatever uncertainty we are in, or whatever mistakes may arise about the time of Christ's coming, that coming itself is certain. This has been the faith and hope of all Christians in all ages of the church; it was the faith and hope of the Old Testament saints.

All believers will be gathered together to Christ, to be with him, and to be happy in his presence forever. We should firmly believe the second coming of Christ; but there was a danger that the Thessalonians, being mistaken about the time, might question the truth or certainty of the coming itself. False doctrines are like the winds that toss the water to and fro; and they unsettle the minds of people, which are as unstable as water. It is enough for us to know that our Lord will come and will gather all his saints to him.

A reason why they should not expect the coming of Christ as near is given. There would be a general falling away first, that would cause the rise of antichrist, that man of sin. There have been great disputes about who or what is intended by this man of sin and son of perdition. The man of sin not only practices wickedness but also promotes and commands sin and wickedness in others; and is the son of perdition, because he is destined for certain destruction and is the instrument to destroy many others, both in soul and body.

As God was in the temple in ancient times and worshipped there, and is in and with his church now; so the antichrist mentioned here is a usurper of God's authority in the Christian church, who claims Divine honors.