2 Thessalonians provides a warning to Christians to keep active in their faith, despite the persecution they face. The letter seems to be a response to the rumor -- or maybe even actual teaching -- that this suffering is part of the "birth pangs" that have been prophesied to accompany the return of Jesus and the coming Day of the Lord. It is not.And Christians need to be aware of the enormous stakes of understanding the truth about Jesus' return, which will bring about judgment on all who have not been faithful. This will lead to eternal punishment and destruction for the unfaithful -- a complete and permanent separation from God. Christians need to do whatever is necessary to prevent them from falling into the group who will receive eternal punishment.
This leads to almost paranoid fears of the ways that Christians could be lead astray -- by untrue teaching, by the leader of evil on earth (who in Revelation will be called the Antichrist), or even by other Christians who have picked up bad or dangerous habits. The deeper reminder, though, is that faith means seeking, spreading, and living out the truth of Jesus Christ, not just waiting on Jesus to come back.
