Charles Ellicott Commentary 2 Thessalonians 1:5

"[which is] a manifest token of the righteous judgment of God; to the end that ye may be counted worthy of the kingdom of God, for which ye also suffer:" — 2 Thessalonians 1:5 (ASV)

Which is... — In the fervent eloquence of the original, these connecting words are omitted, and the clause is added in apposition to the words “in all your persecutions.” The effect is similar to using a dash in English: “which you endure—a manifest token.” The indication of God’s righteous judgment comes not so much from the vitality and growth of the Thessalonians’ faith and love, but from the very fact that they were being persecuted. Such persecution was an actual sign of how God's fair judgment would unfold on the last day. We should not place undue stress on the word “righteous,” as if it meant “a token of the righteousness of God’s judgment.” The point is simply to indicate what a fair judge would likely decide.

That you may be counted worthy — This phrase expresses the result not of God’s future judgment, but of the patient suffering that reveals what that judgment will be. The “counting worthy” (or perhaps, the “declaring worthy”) is, in fact, the judgment or sentence itself. It is as if to say, “You suffer in such a way that we can foresee God’s fair verdict: namely, that you will be declared fit to receive God’s kingdom.” (The Greek tense points to a distinct moment when this declaration is made.) In this context, the phrase “counted worthy” has nothing to do with the theological question of merit.

The kingdom of God — This was a prominent feature of the initial preaching at Thessalonica (see Introduction to the First Epistle to the Thessalonians). Are the Thessalonian Christians, then, not yet in the kingdom of God? Yes, but only as its subjects. In the future, they are to be counted worthy not of admission into the kingdom, but of the kingdom itself—that is, to inherit it and become its kings (compare to the parallel argument in 2 Timothy 2:12).

For which you also suffer — Paul was very fond of using “also” in relative clauses. It tightens the connection between the relative and antecedent clauses, bringing out more clearly the vital link between suffering and reigning. They suffer “for the kingdom,” not merely to win it, but on its behalf: in its defense, as a consequence of being its citizens, and to extend its dominion.