I don't believe the restrainer (2 Thessalonians 2:7-8) can be the Holy Spirit working through the church because many of us Christians will still be on the earth during the Antichrist's rule (Revelation 13:7-10, 14:12-13), and no one can be a Christian without the Spirit (Romans 8:9), and there are no Christians outside of the church (Ephesians 4:4-6).

I believe if Satan can be restrained by an angel (Revelation 20:1-3), then a man (the Antichrist) can be restrained by an angel also.

The restrainer could be the archangel Michael, or it could be another angel over another nation. We see the connection between angels and nations in Daniel. Daniel is told that Michael is "the great prince which standeth for the children of thy people" (Daniel 12:1), that is, Michael is over the nation of Israel. There are other angels over other nations: "The prince of the kingdom of Persia withstood me one and twenty days: but, lo, Michael, one of the chief princes, came to help me... now will I return to fight with the prince of Persia: and when I am gone forth, lo, the prince of Grecia shall come" (Daniel 10:13, 20).

The restrainer may be the angel and nation that are keeping the Antichrist from taking over the Middle East and Europe: in Paul's day it would have been the Roman Empire; today it would be the United States. I believe that the United States will have to be removed as a superpower in the world before the Antichrist can take over the Middle East and Europe.

Note that unlike the NIV, the Greek doesn't say the restrainer holds "it" (the mystery of iniquity) back, for "the mystery of iniquity doth already work." What the restrainer is holding back is the Antichrist, that "he" might be revealed in "his" time, for when the restrainer is removed, then shall the Antichrist be revealed: "And now ye know what withholdeth that he might be revealed in his time. For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way. And then shall that Wicked be revealed" (2 Thessalonians 2:6-8).