Gr. endeigma, “evidence,” “proof,” “token” (cf. on Phil. 1:28, where a related word, endeixis, is used). It is not the persecutions and tribulations that are proof of the righteous judgment of God, but rather the attitude of the believers toward such affliction. Patient endurance and courageous faith under persecution, being the result of God‘s grace, are evidence of His present interest and care for the sufferers, and thus proof that He will finally reverse the injustices of the world (cf. Eccl. 3:16, 17).

 This may be applied to God‘s interposition on behalf of His people (v. 6), and to the great judgment whose execution is portrayed in vs. 7-10 (see on Ps. 73:3-24; Rom. 2:5). The fortitude of the persecuted saints is to the wicked an omen of their own coming destruction (cf. on Phil. 1:28).

 The Christian is not of himself worthy of the kingdom of God, nor do sufferings necessarily make him so. There is nothing he can do to merit the kingdom of God (cf. on Eph. 2:8), but by God‘s forgiving grace he is deemed worthy (cf. on Rom. 6:23).

 The expression, as here used, is generally considered synonymous with “heaven” (cf. on Matt. 4:17).

 Or, “you, too, are suffering.” Paul realizes that the apostles are not the only sufferers, but that the Thessalonians even then were enduring persecution for the kingdom‘s sake.