1 John Introduction

Authorship

The book is without autograph but it is unquestionably the work of the Apostle John, ikely written near the end of the first century, perhaps in the 80s A.D. First, the numerous phrases found in the book are common to both this letter and the Gospel of John.  

“To walk in darkness" (2:11 compare to John 8:12)
“Children of God" (3:2 compare to John 11:52)
“To be born of God"  (3:9 compare to John 1:13)
“The Spirit of truth" (4:6 compare to John 14:17; 15:26; 16:13)
“The only begotten Son" (4:9 compare to John 3:16)
“The Savior of the world" (4:14 compare to John 4:42)
“Water and the blood" (5:6 compare to John 19:34)

Second, the author was eyewitness to Jesus' death and resurrection (1:1).

Audience

Irenaeus, an early church father, claimed John to have given the later years of his life to the church at Ephesus as the overseer. John, aware that false teachers had intruded into the church (Acts 20:29-30), and having convinced some believers to withdraw from the fellowship, writes this letter to correct the problem among the Ephesian believers.  

Their false teaching centers around two heresies concerning the Person of Christ—one group denying Jesus as being the Christ (2:22) and the other group denying Jesus had come in the flesh (4:2-3).

Whenever the Person of Jesus is threatened, all kinds of problems arise because to deny Who Jesus is ultimately evolves into a denial of his sovereign Lordship. So the Ephesians were developing a tendency toward lustful lifestyles (2:15-17), leading to denying they were sinning at all (1:5-2:6).

"John combats Docetism {see explanations below} by his insistence on the reality of the humanity of Christ (1:1–3; 4:1–3). He utters severe words against Cerinthianism {see explanations below} by emphasizing the fact that Jesus is the Christ, the Son of God (1:3, 7; 2:22, 23; 3:23; 4:15; 5:1, 20)." [Dunnett, W. M. (2001). Exploring the New Testament (p. 94). Wheaton, IL: Crossway Books.]

"Docetism; taught that Christ appeared as a real man, but He was not. He did not have a real material body. Rather, His appearances were similar to the theophanies or Christophanies of the Old Testament. Cerinthian; taught that the spirit of the divine Christ descended upon the man Jesus at baptism, indwelt Him for the duration of His ministry, and left Him shortly before His crucifixion." [Gromacki, R. G. (1974). New Testament Survey (pp. 369–370). Grand Rapids, MI: Baker Academic.]

Purpose

The obvious reason John wrote the book was to correct false teaching, which was leading to false practices, specifically as the false teaching concerned the Person of Jesus. His desire in correcting the errors in what they were being taught was to restore the assurance of the believer. The phrase "we know" was used by John thirteen times (2:3, 5, 29; 3:14, 16, 19, 24; 4:13, 16; 5:15, 18, 19, 20). The whole book is developed around the theme of producing conviction in the hearts of those who have put their faith in Christ. John wanted every one of them fully assured that it was the work of the true Christ that had changed them. The work of salvation had deeply changed who they were.

John wrote his Gospel to create faith in Jesus Christ so those who believed would experience life (John 20:31). John wrote this Letter (1John) to give those who believe the assurance that their faith was genuine, from God, leading them to possess eternal life (5:13).