Summary: 1) An accurate belief in the nature of God (1 John 1:5), and 2) A genuine belief in the certainty of sin (1 John 1:6, 8, 10)
Ever since the fall, humanity has tried to deny the reality of sin, even though every human being is innately aware of its presence. (cf. Rom. 2:14-16). People today minimize and redefine sin, often alleging that the “failures” of their lives and certain “disorders” exist because of how others have treated them. The victim mentality reigns supreme as popular culture comforts itself in affirming that people are basically good and whatever may be wrong is not really wrong, but merely a preference of personal freedom. Instead of accepting responsibility for their behavior, people demand to be accepted as they are. They reclassify serious and heart issues “illnesses” and “addictions” and try to “cure” them with prescription drugs and psychotherapy. But because that fails to deal with sin, the actual root cause of the problem, society goes from bad to worse. Jesus said that every person is sinful at the very core of his or her being (Mark 7:20–23; cf. Gen. 6:5; Jer. 17:9; James 1:15; 4:1). Many in the church today seem to be reluctant to make the diagnosis Jesus did, for fear they might offend someone or be deemed “unloving.” Thus, sin is explained away in culturally acceptable terms
The apostle John faced a similar situation in the churches to whom he wrote his letter. Flooding into Ephesus and the other cities and churches of Asia Minor were deceitful, sin-denying false teachers (cf. 2:18; 4:1–3; 2 Peter 2:1–2; Jude 4). John had to contend with Greek philosophical dualism (the basis of Gnosticism)—a view that denied the reality of sin and evil. Those who held to this mystical, elitist philosophy argued the spiritual was always good and the physical was always bad; they therefore created an artificial dichotomy between the spiritual realm and the physical world—contending that spiritual realities were all that mattered, and that what was done in the flesh (including sin) was a nonissue. Having written of fellowship and joy in Christ, John raises three false claims that have been made by the Docetists: that sin does not matter (1:6); that it is not a part of our nature (1:8) and that it is not a part of our conduct (1:10) (Barnes, P. (1998). Knowing Where We Stand: The Message of John’s Epistles (p. 19). Darlington, England: Evangelical Press.)
In order to protect against false teaching, people must test what they read, hear and see in order to distinguish what is true from counterfeit. Making that fundamental distinction is essential to the church’s protection and spiritual growth. The wheat must be differentiated from the tares (cf. Matt. 13:24–30), the sheep distinguished from the goats, or people will never be protected from the deadly deceptions of false teachers.
In these verses, John presents two crucial doctrinal tests to determine who is genuine. In order to Measure your Faith properly one must have: 1) An accurate belief in the nature of God (1 John 1:5), and 2) A genuine belief in the certainty of sin (1 John 1:6, 8, 10)