Ephesus had a blend of confusing philosophies and devotions. Light was an essential element to aid people in their quest for gnosis. There have been debates as to whether or not gnosis was “full blown” near the end of the first century. Some say apostolic epistles couldn’t be addressing gnosis influence in the church. Regardless, many were teaching versions of Christianity that strayed from founding doctrines.
1 John is one of those letters to the brethren that distinguishes error from founding doctrines. The founding doctrines declared that Jesus lived among the Jews in all the reality of human life. He ate and drank, walked and talked, and experienced life as mundane as you and I. He physically suffered the cross and physically rose from the tomb. This is something that many who championed Christ would rail against, because they promoted a different version of Christ than the apostles. John would label these as “anti-Christ.” To these Jesus was no more than one in a list of “light bringers” and not the reality of the only sovereign God. To these Jesus was a liberator not from the consequences of sin but from ignorance of gnosis. John wrote in 1:5 “And this is the message we have heard from Him and announce to you, that God is Light, and in Him there is no darkness at all.” It appears that John declares God is the revelation people have been ignorant of, because they have not recognized Jesus as the true incarnate God (cf. 1:3).
“If we say that we have fellowship with Him and yet walk in darkness, we lie and do not practice the truth. If we walk in the light as He Himself is in the Light, then we have fellowship one with another and the blood of His Son cleanses us from all sin” (1:6-7). According to John, God is light. People must walk in God if they are to have fellowship with Him. By walking in Him they have the benefit of cleansing from sin. The vehicle by which people can walk in God is Jesus Christ. For John, souls that were practicing the truth were souls whose faith rested in Jesus for salvation from sin, and eternal life (cf 5:13). For John, those who pursued mysteries (gnosis) and disconnected Jesus from an actual human life and an actual human death and an actual human resurrection, those John says, walk in darkness. They lie. They cannot receive the benefit of sin cleansing. They are “anti-Christ” (2:21-23; 4:1-4).
Many interpreters today view “walking in the light” as moral performance. Many fail to recognize the distinction John makes between believers and unbelievers and portray John as though he were bolstering Christian behavior. While John certainly wouldn’t have opposed greater sanctification, he’s not aiming his readers toward that in the first chapter. To stress “walking in the light” as mere sanctification disregards the crisis of apostasy through “antichrist” spirits. Believers have the benefit of cleansing from sins. If John were equating “walking in the light” with proper moral behavior then every time a believer sinned it would mean they were walking in darkness, and there is no cleansing and no fellowship for those who walk in darkness.
Consider 2 John; 1 Timothy 4:1-3; 2 Timothy 3:1-5; Acts 20:28-30.