Verse 21. Prove all things. Subject everything submitted to you to be believed to the proper test. The word here used (dokimazete,) is one that is properly applicable to metals, referring to the art of the assayer by which the true nature and value of the metal is tested. See Barnes "1 Co 3:13".

This trial was usually made by fire. The meaning here is, that they were carefully to examine everything proposed for their belief. They were not to receive it on trust; to take it on assertion; to believe it because it was urged with vehemence, zeal, or plausibility. In the various opinions and doctrines which were submitted to them for adoption, they were to apply the appropriate tests from reason and the word of God; and what they found to be true they were to embrace; what was false they were to reject. Christianity does not require men to disregard their reason, or to be credulous. It does not expect them to believe anything because others say it is so. It does not make it a duty to receive as undoubted truth all that synods and councils have decreed; or all that is advanced by the ministers of religion. It is, more than any other form of religion, the friend of free inquiry, and would lead men everywhere to understand the reason of the opinions which they entertain. Comp. Ac 17:11,12; 1 Pe 3:15.

Hold fast that which is good. Which is in accordance with reason and the word of God; which is adapted to promote the salvation of the soul and the welfare of society. This is just as much a duty as it is to "prove all things." A man who has applied the proper tests, and has found out what is truth, is bound to embrace it and to hold it fast. He is not at liberty to throw it away, as if it were valueless; or to treat truth and falsehood alike. It is a duty which he owes to himself and to God, to adhere to it firmly, and to suffer the loss of all things rather than to abandon it. There are few more important rules in the New Testament than the one in this passage. It shows what is the true nature of Christianity, and it is a rule whose practical value cannot but be felt constantly in our lives. Other religions require their votaries to receive everything upon trust; Christianity asks us to examine everything. Error, superstition, bigotry, and fanaticism attempt to repress free discussion, by saying that there are certain things which are too sacred in their nature, or which have been too long held, or which are sanctioned by too many great and holy names, to permit their being subjected to the scrutiny of common eyes, or to be handled by common hands. In opposition to all this, Christianity requires us to examine everything -- no matter by whom held; by what councils ordained; by what venerableness of antiquity sustained; or by what sacredness it may be invested. We are to receive no opinion: until we are convinced that it is true; we are to be subjected to no pains or penalties for not believing what we do not perceive to be true; we are to be prohibited from examining no opinion which our fellow-men regard as true, and which they seek to make others believe. No popular current in favour of any doctrine; no influence which name and rank and learning can give it, is to commend it to us as certainly worthy of our belief. By whomsoever held, we are to examine it freely before we embrace it; but when we are convinced that it is true, it is to be held, no matter what current or popular opinion or prejudice may be against it; no matter what ridicule may be poured upon it; and no matter though the belief of it may require us to die a martyr's death.

{h} "Prove" 1 Jo 4:1 {i} "hold fast" Php 4:8