Question: "What does it mean to test everything (1 Thessalonians 5:21)?"
Answer: As Paul concludes his first letter to the Thessalonians, he offers some varied ethical instructions including that his readers should test everything (1 Thessalonians 5:21) and hold to what is good. While this certainly stands on its own as an important principle, it seems that Paul had something more particular in mind, as those words immediately follow his instruction not to despise prophetic utterances (1 Thessalonians 5:20). John adds some helpful information as he likewise encourages his readers not to believe every spirit but to test them to see whether they are from God, because many false prophets had gone out into the world (1 John 4:1).
Paul writes to the Thessalonians around AD 51, and at that time God was using the gift of prophecy to communicate His Word until His revelation would be completed by the apostles. In 1 Corinthians 13:10, Paul indicates that there would be a conclusion to these revelatory gifts, as, when the complete comes (to telion), the partial would be done away. Peter adds that God moved particular men and they spoke from God (2 Peter 1:20–21). While not all agree that 1 Corinthians 13:10 is referring to the completion of God’s revealed Word to humanity, many would agree that at least Paul is referring to a time when God would no longer use special giftings to communicate His Word. When Paul writes in the mid-first century, and John after him a couple of decades later, it is evident that those revelatory gifts are still in play, as both Paul and John caution their readers to test everything (1 Thessalonians 5:21). Particularly, believers were to test prophecies and spirits of prophecy (1 John 4:1) to see whether the message and the messenger were indeed from God. The first century required a unique kind of discernment, because God’s revealed Word (the Bible) was not completed until nearly the end of the first century, when John penned the book of Revelation between AD 85 and 95.
Even though believers now can read the Bible and have confidence that they are reading God’s completed Word, there is still need for discernment, and Paul’s instruction to test everything (1 Thessalonians 5:21) is still pertinent today. There are still many alleged applications of Scripture that need to be examined and tested to see if they arise from the Author’s intended meaning or if they are contrivances of those who are not handling the Bible well. There are also many who claim to speak for God today. One must test these claims in light of the Scriptures.
Paul and John gave significant attention to guarding and protecting believers from false teaching, as they knew of the existence of influential counterfeits and false teachers. Paul warns Timothy to be on guard against falsehood (1 Timothy 6:20; 2 Timothy 4:15). John warns his readers to be on guard against idols (1 John 5:21). Peter adds that believers should be on guard so they are not carried away by error (2 Peter 3:17). Testing everything and holding fast to what is good (1 Thessalonians 5:21) remains an important discipline for every believer, in all eras.