Everyone who practices sin also practices lawlessness; and sin is lawlessness. You know that He appeared in order to take away sins; and in Him there is no sin. No one who abides in Him sins; no one who sins has seen Him or knows Him. Little children, make sure no one deceives you; the one who practices righteousness is righteous, just as He is righteous; the one who practices sin is of the devil; for the devil has sinned from the beginning. The Son of God appeared for this purpose, to destroy the works of the devil. No one who is born of God practices sin, because His seed abides in him; and he cannot sin, because he is born of God. By this the children of God and the children of the devil are obvious: anyone who does not practice righteousness is not of God, nor the one who does not love his brother.  1 John 3:4–10

Throughout its history the true church has always maintained that Scripture clearly sets forth certain basic standards of belief and behavior as necessary marks of genuine saving faith. An affirmation and acceptance of the biblical gospel, and a life that is characterized by a worthy walk, have rightly been seen as accurate indicators of the work of the Trinity on a person’s heart. And when such fruit is absent in an individual’s life, the church has appropriately called into question his or her profession of faith.

In recent decades, however, that has begun to change. More and more so-called evangelicals have downplayed the significance of biblical doctrine—even such crucial doctrines as the person of Christ and justification by faith alone. Incredibly, some have even asserted that the lost can be saved apart from any knowledge of the gospel at all, arguing that if pagan people merely live up to whatever standards of religion, morality, and ethics they have, God will accept them. Since they claim there are scarcely any doctrinal necessities, there can hardly be any behavioral ones.

The apostle John would have been appalled by such contemporary evangelical equivocation. He wrote clearly and unmistakably that saving faith involves accepting certain essential doctrines—such as the Trinity and the substitutionary work of Christ on the cross—and results in certain essential actions—including repentance from sin, obedience to the Word, a desire to walk as Christ walked (live righteously), love for the brethren, and a hatred for the evils of the world and the flesh. John and all the writers of the New Testament taught that unless a person believes and practices such truths, he or she is not saved, no matter what he or she might claim. Bad theology damns, and bad behavior reveals bad theology. Yet, in spite of the unmistakable clarity with which this is presented in both this epistle (No one who is born of God practices sin [3:9a]) and the rest of the New Testament, a significant cross section of contemporary Christendom remains unpersuaded and confused concerning the truth.

For example, some commentators say the apostle was exhorting lawless, misbehaving Christians to rededicate their lives to the Lord and move from immature, carnal behavior to spirituality. In this way, they attempt to tone down the letter and make it less definitive or harsh. But their arguments cannot account for John’s clear purpose for writing the letter (in 5:13), which was to enable his readers to examine themselves so that they might know whether or not their faith was saving. The dichotomy John presents is not deeper faith versus shallower faith, but rather a saving faith versus a non-saving one.

MacArthur, John. 1, 2, 3 John. MacArthur New Testament Commentary. Chicago, IL: Moody Publishers, 2007.