What Does 1 Thessalonians 5:18 Mean?

In every thing give thanks: for this is the will of God in Christ Jesus concerning you—en panti euchareisteite; touto gar thelēma Theou en Christō Iēsou eis hymas (ἐν παντὶ εὐχαριστεῖτε· τοῦτο γὰρ θέλημα Θεοῦ ἐν Χριστῷ Ἰησοῦ εἰς ὑμᾶς). En panti (ἐν παντί, 'in everything') is comprehensive—not 'for everything' (suggesting thanksgiving for sin or evil) but 'in everything' (maintaining thankful spirit amid all circumstances). Eucharistia (εὐχαριστία, 'thanksgiving') flows from recognizing God's sovereign goodness even when circumstances appear bad.

For this is the will of God in Christ Jesus concerning you—Christians seek God's will regarding vocation, marriage, location; Paul declares it plainly: rejoice evermore (v. 16), pray without ceasing (v. 17), give thanks in everything (v. 18). These three commands constitute God's will 'in Christ Jesus'—not apart from Christ but through union with Him. Only Christ-connection enables constant joy, unceasing prayer, and universal thanksgiving. Apart from Christ, circumstances dictate emotions; in Christ, gospel truth sustains joy, prayer, and thanksgiving regardless of circumstances. These aren't personality traits (some are 'naturally' joyful or thankful) but Spirit-produced fruit available to all believers.