After that, though, just as in the first chapter, Paul says it's the right thing to give thanks. This time it's for God's election of these brothers and sisters to salvation. And Paul was privileged to be the one who shared the good news that they responded to. That sharing of the gospel is the call to salvation.
There's something important to look at about God's choice, and about salvation in this passage. Here's the translation from the NET Bible:
"But we ought to thank God always for you, brothers and sisters loved by the Lord, because God chose you from the beginning for salvation through sanctification by the Spirit and faith in the truth. He called you to this salvation through our gospel, so that you may possess the glory of our Lord Jesus Christ." (2 Thessalonians 2:13,14 NET)
There are those who focus on the word "chose" in this passage. I think it is an important word, especially when one looks at the subject of this verb: God. But of equal importance, is the object of the sentence and the modifiers to that choice. The object is "you" (the Thessalonians) but applies equally to us. But what were we chosen for? Salvation. How? Through the Spirit's setting us apart, and faith in the truth. What truth? Well, the truth in the good news that Paul shared with them, the way in which they were called to salvation. That truth is Jesus, "the way, the truth, and the life." Paul put it this way in Romans 5:8: "But God demonstrates his own love for us, in that while we were still sinners, Christ died for us."
In other words, God has chosen us for salvation -- this is what we are meant for. That salvation, however, comes in response to a call for us to respond to. God has done the work as Christ on the cross, but He also insists that we must receive that work in belief that He's done the work.
So why is Paul thankful? So much so that he "shoulds" on himself. I think the answer is two-fold. The primary reason, because it is so much larger, is that God didn't have to do this for us. It's His unfathomable love for us that lead to such a gracious act. He really had only one requirement set forth in the garden -- show your understanding of Who I am by being obedient in one thing only. And Eve and Adam both failed. As have we. Paul knows further, that Israel continued to fail in its task to be the people God asked them to be -- His chosen ones who would receive the benefit of His grace as a covenant promise. And Israel failed to keep the covenant. And so God fulfilled the covenant through His Son, Jesus. And every follower of Jesus gets what God wanted all along for us -- to be set apart, living set apart lives, holy as God is holy. This is a really big thing and it's no wonder Paul once again gives thanks to God.
I think Paul was also thankful that his labor played a part in the state of the Thessalonians. He was able to give the call they responded to. How cool is that? While some folks seem to have a problem with the idea of "evangelism", which is nothing more than sharing what's important in your life, imagine the added measure of thanksgiving you'd have if your own sharing was the call that someone finally heard and responded to. (I don't think Paul is discounting the work of the Holy Spirit, and neither am I.)
Paul was a person who had much to be thankful for. Catch a glimpse Thessalonians. He might have said, "I praise God that you are saved. Do you see that? It's bigger than anything else. Remember it, and stand firm in the face of adversity."