Prove all things; hold fast that which is good.

People's New Testament

5:21 Prove all things. What was spoken they must put to the test, they must hold fast to. There were those who could discern spirits (1Co 12:10). There were also rules for testing (1Jo 4:1-8).

Wesley's Notes

5:21 Meantime, prove all things - Which any preacher recommends. (He speaks of practice, not of doctrines.) Try every advice by the touchstone of scripture, and hold fast that which is good - Zealously, resolutely, diligently practise it, in spite of all opposition.

Jamieson-Fausset-Brown Bible Commentary

21, 22. Some of the oldest manuscripts insert "But." You ought indeed not to "quench" the manifestations of "the Spirit," nor "despise prophesyings"; "but," at the same time, do not take "all" as genuine which professes to be so; "prove (test) all" such manifestations. The means of testing them existed in the Church, in those who had the "discerning of spirits" (1Co 12:10; 14:29; 1Jo 4:1). Another sure test, which we also have, is, to try the professed revelation whether it accords with Scripture, as the noble Bereans did (Isa 8:20; Ac 17:11; Ga 1:8, 9). This precept negatives the Romish priest's assumption of infallibly laying down the law, without the laity having the right, in the exercise of private judgment, to test it by Scripture. Locke says, Those who are for laying aside reason in matters of revelation, resemble one who would put out his eyes in order to use a telescope.

hold fast that which is good-Join this clause with the next clause (1Th 5:22), not merely with the sentence preceding. As the result of your "proving all things," and especially all prophesyings, "hold fast (Lu 8:15; 1Co 11:2; Heb 2:1) the good, and hold yourselves aloof from every appearance of evil" ("every evil species" [Bengel and Wahl]). Do not accept even a professedly spirit-inspired communication, if it be at variance with the truth taught you (2Th 2:2).

Matthew Henry's Concise Commentary

5:16-22 We are to rejoice in creature-comforts, as if we rejoiced not, and must not expect to live many years, and rejoice in them all; but if we do rejoice in God, we may do that evermore. A truly religious life is a life of constant joy. And we should rejoice more, if we prayed more. Prayer will help forward all lawful business, and every good work. If we pray without ceasing, we shall not want matter for thanksgiving in every thing. We shall see cause to give thanks for sparing and preventing, for common and uncommon, past and present, temporal and spiritual mercies. Not only for prosperous and pleasing, but also for afflicting providences, for chastisements and corrections; for God designs all for our good, though we at present see not how they tend to it. Quench not the Spirit. Christians are said to be baptized with the Holy Ghost and with fire. He worketh as fire, by enlightening, enlivening, and purifying the souls of men. As fire is put out by taking away fuel, and as it is quenched by pouring water, or putting a great deal of earth upon it; so we must be careful not to quench the Holy Spirit, by indulging carnal lusts and affections, minding only earthly things. Believers often hinder their growth in grace, by not giving themselves up to the spiritual affections raised in their hearts by the Holy Spirit. By prophesyings, here understand the preaching of the word, the interpreting and applying the Scriptures. We must not despise preaching, though it is plain, and we are told no more than what we knew before. We must search the Scriptures. And proving all things must be to hold fast that which is good. We should abstain from sin, and whatever looks like sin, leads to it, and borders upon it. He who is not shy of the appearances of sin, who shuns not the occasions of it, and who avoids not the temptations and approaches to it, will not long keep from doing sin.

Matthew Henry's Whole Bible Commentary

Verses 16-22

Here we have divers short exhortations, that will not burden our memories, but will be of great use to direct the motions of our hearts and lives; for the duties are of great importance, and we may observe how they are connected together, and have a dependence upon one another. 1. Rejoice evermore, v. 16. This must be understood of spiritual joy; for we must rejoice in our creature-comforts as if we rejoiced not, and must not expect to live many years, and rejoice in them all; but, if we do rejoice in God, we may do that evermore. In him our joy will be full; and it is our fault if we have not a continual feast. If we are sorrowful upon any worldly account, yet still we may always rejoice, 2 Co. 6:10. Note, A religious life is a pleasant life, it is a life of constant joy. 2. Pray without ceasing, v. 17. Note, The way to rejoice evermore is to pray without ceasing. We should rejoice more if we prayed more. We should keep up stated times for prayer, and continue instant in prayer. We should pray always, and not faint: pray without weariness, and continue in prayer, till we come to that world where prayer shall be swallowed up in praise. The meaning is not that men should do nothing but pray, but that nothing else we do should hinder prayer in its proper season. Prayer will help forward and not hinder all other lawful business, and every good work. 3. In every thing give thanks, v. 18. If we pray without ceasing, we shall not want matter for thanksgiving in every thing. As we must in every thing make our requests known to God by supplications, so we must not omit thanksgiving, Phil. 4:6. We should be thankful in every condition, even in adversity as well as prosperity. It is never so bad with us but it might be worse. If we have ever so much occasion to make our humble complaints to God, we never can have any reason to complain of God, and have always much reason to praise and give thanks: the apostle says, This is the will of God in Christ Jesus concerning us, that we give thanks, seeing God is reconciled to us in Christ Jesus; in him, through him, and for his sake, he allows us to rejoice evermore, and appoints us in every thing to give thanks. It is pleasing to God. 4. Quench not the Spirit (v. 19), for it is this Spirit of grace and supplication that helpeth our infirmities, that assisteth us in our prayers and thanksgivings. Christians are said to be baptized with the Holy Ghost and with fire. He worketh as fire, by enlightening, enlivening, and purifying the souls of men. We must be careful not to quench this holy fire. As fire is put out by withdrawing fuel, so we quench the Spirit if we do not stir up our spirits, and all that is within us, to comply with the motions of the good Spirit; and as fire is quenched by pouring water, or putting a great quantity of dirt upon it, so we must be careful not to quench the Holy Spirit by indulging carnal lusts and affections, or minding only earthly things. 5. Despise not prophesyings (v. 20); for, if we neglect the means of grace, we forfeit the Spirit of grace. By prophesyings here we are to understand the preaching of the word, the interpreting and applying of the scriptures; and this we must not despise, but should prize and value, because it is the ordinance of God, appointed of him for our furtherance and increase in knowledge and grace, in holiness and comfort. We must not despise preaching, though it be plain, and not with enticing words of men's wisdom, and though we be told no more than what we knew before. It is useful, and many times needful, to have our minds stirred up, our affections and resolutions excited, to those things that we knew before to be our interest and our duty. 6. Prove all things, but hold fast that which is good, v. 21. This is a needful caution, to prove all things; for, though we must put a value on preaching, we must not take things upon trust from the preacher, but try them by the law and the testimony. We must search the scriptures, whether what they say be true or not. We must not believe every spirit, but must try the spirits. But we must not be always trying, always unsettled; no, at length we must be settled, and hold fast that which is good. When we are satisfied that any thing is right, and true, and good, we must hold it fast, and not let it go, whatever opposition or whatever persecution we meet with for the sake thereof. Note, The doctrines of human infallibility, implicit faith, and blind obedience, are not the doctrines of the Bible. Every Christian has and ought to have, the judgment of discretion, and should have his senses exercised in discerning between good and evil, truth and falsehood, Heb. 5:13, 14. And proving all things must be in order to holding fast that which is good. We must not always be seekers, or fluctuating in our minds, like children tossed to and fro with every wind of doctrine. 7. Abstain from all appearance of evil, v. 22. This is a good means to prevent our being deceived with false doctrines, or unsettled in our faith; for our Saviour has told us (Jn. 7:17), If a man will do his will, he shall know of the doctrine whether it be of God. Corrupt affections indulged in the heart, and evil practices allowed of in the life, will greatly tend to promote fatal errors in the mind; whereas purity of heart, and integrity of life, will dispose men to receive the truth in the love of it. We should therefore abstain from evil, and all appearances of evil, from sin, and that which looks like sin, leads to it, and borders upon it. He who is not shy of the appearances of sin, who shuns not the occasions of sin, and who avoids not the temptations and approaches to sin, will not long abstain from the actual commission of sin.