Believers must test all things, including long-held notions, and hold fast only to what passes (I Thessalonians 5:21). Many tenaciously follow Revelation 3:11's instruction to hold fast while ignoring the instruction to test first. Familiarity and comfort do not justify clinging to an old idea, such as "watch world news" for Luke 21:36, without a solid biblical foundation. Experience proves that not everything held for decades is true; a Sunday rather than a Monday Pentecost is one example. Beliefs must be tested continually and rigorously against the only standard that counts, the Bible. Human nature is lazy and takes the easy road, relying on human reasoning, the word of others, or tradition rather than the hard, humbling work of studying and believing what Scripture actually says. The church's history over recent decades shows the fruits of taking doctrine for granted instead of letting clear scriptures guide understanding. People differ on what the Bible teaches because they come with preconceived ideas, latch onto any verse that seems to support them, and ignore or minimize clear verses that contradict them. God can use this as a test of the heart's true intent, revealing where allegiance lies: in humble submission to His clear instructions, or in men's ideas, which become idols. If a belief cannot be proved from clear, unambiguous scriptures, that is a red flag. Clear scriptures form a solid-rock foundation, while ambiguous ones open to private interpretation form a foundation of sand, and only the former will stand when storms come (Matthew 7:24-27). Letting the Bible interpret itself, rather than adding extra-biblical meanings, keeps one on firm ground.

The proving ground concept, illustrated through Aberdeen Proving Ground's century of testing military technology, provides the framework for understanding how God works with His people. Just as manufacturers test raw materials, designs, and finished products to ensure quality before deployment, God, as the manufacturer of righteous character, tests every person He calls, refusing to pass anyone who does not meet His standard of righteousness. This testing occurs on the proving ground of human life and forms the culmination of a larger series on God teaching believers to think, based on Romans 12:2: not being conformed to this world, being transformed by renewing the mind, and proving what is the good, acceptable, and perfect will of God. These three elements are not separate stages but one seamless process; rejecting worldly conformity and renewing the mind are the very means by which God's will is proven. The Greek word dokimazo, meaning to test, try, or prove something genuine, is central to this teaching. Illustrated by Jesus's parable of the man testing his oxen, and applied to vetting people for trustworthiness or fitness, this word describes how God tests the genuineness of faith like gold refined by fire, and expects believers to likewise test His way of life to confirm it is trustworthy. Simply learning and accepting God's declarations—the Ten Commandments, the Beatitudes, the fruit of the Spirit—is only a starting point, comparable to a child's exercise. God wants these truths put into practice through real situations, often uncomfortable or costly ones, so they become engraved in character rather than remaining mere mental assent. This principle appears throughout Paul's writings: in 1 Thessalonians 5:21-22 to test all things and hold fast what is good; in Ephesians 5 to prove what is acceptable to the Lord while walking as children of light, producing goodness, righteousness, and truth; and in Philippians 1 to approve the things that are excellent through love, knowledge, and discernment, all for the glory of God. This proving process is not quick or simplistic—it often requires patience, discernment, and time, especially in relationships, since snap judgments can be disastrous. Because time is limited and uncertain, believers are urged to prioritize this work of proving God's will rather than procrastinate. Abraham exemplifies this pattern. Given only bare promises in Genesis 12, he proved God's will by obedience—leaving his homeland, enduring famine, waiting twenty-five years for a promised son, learning through failure about lying and marriage, and ultimately offering Isaac in faith that God could raise him from the dead. Hebrews 11 confirms that Abraham's faith was demonstrated through action, not mere belief. This is the pattern believers must follow: proving God's will both through failure and through righteous success, always thinking, evaluating, and discerning how God is at work. Since believers are being shaped into the image of Christ, they cannot afford careless or lazy thinking but must hone their minds sharply, trusting that God, who began this good work, will bring it to completion through Jesus Christ.

The theme of testing all things emerges as the practical outworking of the central problem addressed in II and III John: how believers are to distinguish true servants of God from false teachers who exploited the early church's custom of hospitality toward traveling preachers. Because common courtesy required Christians to provide for visiting teachers, this created an opening for deceivers and even for outright frauds seeking financial gain, so John's letters supply the tests needed to discern truth from error. II John presents these tests in the broadest terms, applying them to a congregation addressed as "the elect lady and her children," while III John personalizes them through the examples of Gaius, who rightly extended hospitality to true teachers; Diotrephes, who wrongly refused it; and Demetrius, whose conduct was commendable. Three tests recur throughout both letters: the moral test of righteousness or obedience, the social test of love, and the doctrinal test of truth, particularly regarding whether a teacher confesses Jesus Christ as having come in the flesh. Anyone denying this is labeled a deceiver and an antichrist, a term meaning simply one who distorts or opposes the true Christ, whether from inside or outside the congregation. This testing responsibility is not limited to evaluating outsiders but extends to examining everything presented for belief, including teaching within the church itself. The apostle Paul's command in I Thessalonians 5:21, "Test all things; hold fast what is good," functions as the governing principle behind this entire discussion. The Greek term behind "test" refers to the assaying of metals by fire to determine their true value, indicating that every doctrine, opinion, or claim—including statements made by ministers—must be subjected to rigorous scrutiny against Scripture rather than accepted merely because it is delivered with passion or authority. The Bereans exemplify this approach, having searched the Scriptures daily to verify what they were taught. God does not ask for blind acceptance or gullibility but for reasoned examination, followed by firm commitment once truth is confirmed; what is proven true must be held fast, while what is false must be rejected outright, since truth and falsehood cannot be treated as equally valid. This principle stands in direct contrast to mainstream religious systems that demand acceptance of tradition—such as Sunday-keeping, the trinity, or the doctrine of heaven and hell at death—without scrutiny, suppressing free examination in favor of inherited custom or ecclesiastical authority. True Christianity, by contrast, requires examining every teaching regardless of who holds it or what tradition supports it, refusing to be swept along by popular trends or "itching ears" that prefer comfortable fables to sound doctrine. Ultimately, testing all things is tied to the broader call in II and III John to remain steadfast rather than assume that spiritual victories once won need no further vigilance, echoing Paul's warning that one who thinks he stands must take heed lest he fall. Loving the truth, proving it through careful examination, and holding it firmly are inseparable from genuine love for God and for one another, since Christian unity and love are shown to rest not on sentiment but on shared commitment to sound doctrine discerned through diligent testing.