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. "1Cor 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. Acts 17:11, Acts 17:12 1 Pet 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.