Second Thessalonians 2:12-15 presents the simplest explanation of the doctrine of “election” in the bible. “Election” describes how God chose who will be saved and who won’t. This may be THE most misunderstood biblical concept in all of christendom’s various denominations.
Protestant denominations mainly base what they teach about election on what John Calvin wrote about it. Calvin wrote that the way God predestined (“elected”) people for heaven or hell was completely random and arbitrary. (We might compare it to “pulling names out of a hat.”) According to his reasoning, what happens to a soul in eternity has nothing to do with that person’s choices; whether one goes to heaven or hell would depend, essentially, on God’s “mood” in the moment! The practical application of Calvin’s doctrine says that WE have essentially nothing at all to do with our salvation; whether one is saved or not is simply a matter of random chance.
The problem with this doctrine is that it does not match what the new testament says. In this part of 2 Thessalonians, Paul shows that God “chooses” people for salvation (“elects” us) through sanctification by the Spirit AND our own belief in the truth (vs. 13). Note that BOTH of these things are necessary – not merely one or the other. In this context, “sanctification by the Spirit” represents His holy response to our submission to God’s word – NOT some kind of random “enabling” on His part. Verse 14 shows that God “contacts” us through the medium of the gospel, so that we may believe and respond to His will. Verse 15 emphasizes the importance of our continuing in His will; Paul urges the Thessalonians (and, by extension, us) to “stand fast and hold the traditions” that he had taught them. He also points out that it makes no difference whether that teaching took place personally (“face-to-face” via spoken words), or by letter (neither method carries more “weight” than the other).
In chapter 3:6, Paul gives an explicit command regarding how we associate with fellow-Christians who are “out-of-step” with biblical teaching and practice: We are to “withdraw” (literally, keep away from, be on guard against) those who persist in being idle and flouting the “tradition” (body of teachings or instruction) received from Paul and the apostles. Faithfulness to God does not give us the option of a choice in such situations. Apparently, some of the Thessalonian Christians had essentially “retired” from their day-to-day responsibilities (vv. 6-12). These had become so “busy” wasting their time as idle busybodies (vs. 11) that they had begun to “sponge” off more responsible brethren just to have food to eat! (This leads, then, to the instruction in verse 10b, about refusing to feed such folks.) We can see the seriousness with which Paul expected the brethren to treat this situation in verse 14, where the Christians are told to “note” (mark) such a person, in order to avoid fraternizing or “fellowshipping” with him/her so that this person would be ashamed of their misbehavior. Far from teaching us to “be mean” to apostate Christians, verse 15 shows that Christians are specifically commanded to “warn” (admonish, encourage) them because they’re brethren, and we are forbidden to view them as enemies.