5:19 Quenching the Spirit is a figurative expression used to illustrate the possibility of hindering the Spirit's work in and through the believer. The image is that of water thrown on a fire. The proper response is to follow the Spirit's direction and control without resistance (v. 18; cf. Gal. 5:16, 25). The next verse gives one way in which believers can quench the Spirit.
5:20-21 There appears to have been a tendency in the Thessalonian church to despise prophetic utterances (i.e., the announcing of some word from God; cf. 1 Cor. 14:1). Paul warned against regarding these words from God as only words from men. However, he also counseled that his readers should test these utterances. They could do this by comparing what the speaker said with the standard of previously given divine revelation (cf. Deut. 13:1-5; 18:20; 1 John 4:1-3). They should retain everything that passed the test. What did not they should reject along with all other kinds of evil.130
5:22 They should also avoid every form of evil (Gr. pantos eidous ponerou). This seems to be the best meaning in view of the contrast with verse 21. The alternative interpretation is that Paul wanted his readers not only to avoid evil itself but that which others might perceive as involving evil (cf. Rom. 14). It is not always possible, of course, to abstain from what appears to extremely narrow-minded people to be evil.
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