I. The Holy Spirit is here spoken of not strictly in respect of His Person, but in respect of His energising power in and on the heart. His workings, the Apostle would say, may be so counteracted as to become ineffectual. They may be quenched as the flame that is kindled for a time, but being neglected, sooner or later expires. Rain, dew, wind, fire, those mysterious agencies of nature, are in Scripture the fitting and effective emblems of the Holy Spirit's power in the hearts and lives of men. Those who are already believers are, in regard to their advancing sanctification, to cherish His manifestations. By relapse into sinful indulgences, the follower of Jesus quenches the spirit of grace within his heart.
II. "Despise not prophesyings." The Spirit is the Divine power, prophesyings are the human instrumentality. If men would be kept from quenching the one, they must be kept from thinking meanly of the other. The Spirit is the Divine light: if they would retain it, they must be careful to preserve prophesyings, the lamp in which it is placed.
III. The next clause links itself on to that which precedes it. So far from Undervaluing or spurning prophecies, believers are urged to test them. As there are counterfeits of the truth in circulation, it is wise on the part of all who would buy the truth to test it, to submit it to careful examination, so that they may not be deceived, but may become possessors of that priceless treasure, gold tried in the fire, that finest gold which alone can make truly rich.
IV. The holding fast of the good exists only where there is an abhorring of that which is evil. Hence follows the closing exhortation: "Abstain from every form of evil." While the first reference is to evil elements, which might appear in the prophesyings, it purposely expands so as to embrace every kind of evil into contact with which the follower of Christ may be brought. In regard to all moral evil, he is enjoined to keep himself unspotted from the world.
J. Hutchison, Lectures on Thessalonians,p. 226.
Reference: 1 Thessalonians 5:20. Good Words,vol. iii., p. 698.