The young, Thessalonian believers were crippled by fear concerning the ultimate outcome of their faith. They wondered, “Will I fall away in the rebellion and ultimately receive condemnation when Christ returns (2 Thess. 2:10-12)? Or, will I be able to stand firm against the satanic workings of the Antichrist and be able to hold to the truth of the gospel (2 Thess. 2:15). Or, will I ultimately believe what is false (cf. 2 Thess. 2:11)." These questions plagued Paul's young converts in the faith.

So, as a faithful shepherd of his sheep, Paul assures them that their ultimate outcome is glorification (2 Thess. 2:14). Paul's assurance is intended to motivate the Thessalonians (and us!) to stand firm and hold to the traditions which they were taught by Paul, Silas and Timothy (2 Thess. 2:15). 

Yet, Paul knows that the Thessalonians need the continual empowerment of God in order to stand firm and hold to the Apostolic traditions, which they were taught. So, he concludes chapter 2 with a prayer for inner strength in vv. 16-17. What he calls on the Thessalonians (and us!) to do in v. 15 (stand firm and hold to the Apostolic tradition), he prays for God to give.