2 Thessalonians 1:5

Having mentioned their persecutions and tribulations, which they endured principally for the cause of Christ, the apostle proceeds to offer several things for their comfort under them; as, I. He tells them of the present happiness and advantage of their sufferings, Th2 1:5. Their faith being thus tried, and patience exercised, they were improved by their sufferings, insomuch that they were counted worthy of the kingdom of God. Their sufferings were a manifest token of this, that they were worthy or meet to be accounted Christians indeed, seeing they could suffer for Christianity. And the truth is, Religion, if it is worth any thing, is worth every thing; and those either have no religion at all, or none that is worth having, or know not how to value it, that cannot find in their hearts to suffer for it. Besides, from their patient suffering, it appeared that, according to the righteous judgment of God, they should be counted worthy of the heavenly glory: not by worthiness of condignity, but of congruity only; not that they could merit heaven, but they were made meet for heaven. We cannot by all our sufferings, any more than by our services, merit heaven as a debt; but by our patience under our sufferings we are qualified for the joy that is promised to patient sufferers in the cause of God. II. He tells them next of the future recompence that shall be given to persecutor and persecuted. 1.

— Matthew Henry's Concise Commentary (public domain)

Which--Your enduring these tribulations is a "token of the righteous judgment of God," manifested in your being enabled to endure them, and in your adversaries thereby filling up the measure of their guilt. The judgment is even now begun, but its consummation will be at the Lord's coming. David (Psa 73:1-14) and Jeremiah (Jer 12:1-4) were perplexed at the wicked prospering and the godly suffering. But Paul, by the light of the New Testament, makes this fact a matter of consolation. It is a proof (so the Greek) of the future judgment, which will set to rights the anomalies of the present state, by rewarding the now suffering saint, and by punishing the persecutor. And even now "the Judge of all the earth does right" (Gen 18:25); for the godly are in themselves sinful and need chastisement to amend them. What they suffer unjustly at the hands of cruel men they suffer justly at the hands of God; and they have their evil things here that they may escape condemnation with the world and have their good things hereafter (Luk 16:25; Co1 11:32) [EDMUNDS]. that ye may be counted worthy--expressing the purpose of God's "righteous judgment" as regards you. for which--Greek, "in behalf of which ye are also suffering" (compare Act 5:41; Act 9:16; Phi 1:29). "Worthy" implies that, though men are justified by faith, they shall be judged "according to their works" (Rev 20:12; compare Th1 2:12; Pe1 1:6-7; Rev 20:4).

— Jamieson-Fausset-Brown Commentary (public domain)