First John is one of five books written by Jesus’ beloved disciple.  It is most likely written after the writing of the Gospel of John.  The purpose of the book seems to be twofold – to refute heresy that has arisen in churches John ministered to and to reassure believers by giving them tests by which they can know they are in Christ.  It is likely meant to be circulated among the churches.

Background of John the Apostle (from study of Matthew 10)

• He and his brother James were known as the “Sons of Thunder” (Mk. 3:17) – apparently because of their temperament. It is interesting to contrast this with his writings in I John of love for one another and love for God.
• John’s mother asked Jesus if he and James could sit on Jesus’ right and left in heaven (Matt 20:20-23). The other disciples were not happy about this (Matt 20:24-28).
• Many believe that James’ and John’s mother was Salome and was one of the women who supported Jesus’ ministry (Matt 27:55-56, Luke 8:3), and who watched the crucifixion from a distance – or near the cross (Mk. 15:40, John 15:25). Based on John 15:25, some believe Salome was Mary’s (the mother of Jesus) sister.  In this case, James and John were actually Jesus’ cousins.  It would make sense that Salome had the means to support the ministry based on her husband’s and son’s successful fishing business.  Salome was also one of the women who found the empty tomb (Mark 16:1-8).
• The financial standing of the family may account for John being able to be in the house of the high priest during Jesus’ trial (Jn 18:15-16), as well as the only disciple next to the cross (Jn 19:26-27).
• John was most likely a disciple of John the Baptist before following Jesus (Jn 1:35-42).
• John was known as the disciple whom Jesus loved (Jn 13:23, 19:26, 20:2) – his was apparently a special relationship with Jesus.
• Took Mary – mother of Jesus – into his care after Jesus’ death by Jesus’ command (Jn 19:25-27)
• Most likely had a close friendship with Peter – they seemed to be the inner circle of the inner circle. Lk 22:7-13 = Jesus sent them to prepare the Passover meal on the night He was betrayed (the last supper).  Jn 18:15-16 = they followed Jesus to the High Priest’s house for His trial.  Jn 20:1-9 = they were the first disciples to see the empty tomb.  Acts 3:1-4:21 = they preached in Jerusalem and were the first to be arrested.  Acts 8:14-15 = sent by the elders in Jerusalem to bestow the Holy Spirit on Samaritans.
• Tradition holds that he ministered for many years into his old age in Ephesus.
• Tertullian wrote that John was banished to Patmos (where he wrote Revelation) after being plunged into boiling oil in Rome and suffering nothing from it.
• His apocalyptic vision may be the fulfillment of Christ’s words in Matt 16:28 that some of his disciples would not see death until seeing Jesus come again.

Heresy
The heresy John addresses is not specifically identified, but several clues in the book point to a teaching that denies the personhood and work of Jesus.  The teaching apparently claims that Jesus did not come in the flesh and did not physically die.  The people teaching this heresy were part of the churches John ministered to but have now divided and left (2:19).  After leaving the churches the same people are now trying to influence and deceive the remaining believers (2:26).

John addresses this heresy in several verses.  He begins the book by rehearsing his credentials as an eyewitness to Jesus’ ministry and making it plain that Jesus was physically here (1:1)  [Note the similarities between the first four verses of I John and the first five verses of the Gospel of John].  He says the liars are the ones who deny that Jesus was the Messiah (2:22).  He tells the believers they need to remember and believe what they were originally told when they first heard the gospel (2:24).  He identifies false teachers as those who deny that Jesus came in the flesh (4:2).

Tests of Faith
John uses several words and phrases repeatedly throughout the book.  When these are noted they clarify many of the tests of faith John gives to his readers.

Lie/Liar/Deceive

• If we say that we have fellowship with Him and yet walk in the darkness, we lie and do not practice the truth (1:6).
• If we say that we have no sin, we are deceiving ourselves, and the truth is not in us (1:8).
• If we say that we have not sinned, we make Him a liar, and His word is not in us (1:10).
• The one who says, “I have come to know Him,” and does not keep His commandments, is a liar, and the truth is not in him (2:4).
• Who is the liar but the one who denies that Jesus is the Christ? (2:22)
• These things I have written to you concerning those who are trying to deceive you (2:26).
• Little children, let no one deceive you; the one who practices righteousness is righteous, just as He is righteous (3:7).
• If someone says, “I love God,” and hates his brother, he is a liar; for the one who does not love his brother whom he has seen, cannot love God whom he has not seen (4:20).
• The one who believes in the Son of God has the witness in himself; the one who does not believe God has made Him a liar, because he has not believed in the witness that God has borne concerning His Son (5:10). 

By this

• And by this we know that we have come to know Him, if we keep His commandments (2:3).
• 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 (3:10).
• We know love by this, that He laid down His life for us; and we ought to lay down our lives for the brethren (3:16).
• We shall know by this (loving in deed and truth – vs. 18) that we are of the truth, and shall assure our heart before Him (3:19).
• And the one who keeps His commandments abides in Him, and He in him. And we know by this that He abides in us, by the Spirit whom He has given us (3:24).
• By this you know the Spirit of God; every spirit that confesses that Jesus Christ has come in the flesh is from God (4:2).
• We are from God; he who knows God listens to us; he who is not from God does not listen to us. By this we know the spirit of truth and the spirit of error (4:6).
• By this the love of God was manifested in us, that God has sent His only begotten Son into the world so that we might live through Him (4:9).
• By this we know that we abide in Him and He in us, because He has given us of His Spirit (4:13).
• By this, love is perfected with us, that we may have confidence in the day of judgment; because as He is, so also are we in this world (4:17).
• By this we know that we love the children of God, when we love God and observe His commandments (5:2).

Why John wrote this Epistle
John goes out of his way to explain why he wrote this letter.  Not all of the explanations are easy to understand on the surface, but careful study will reveal them more clearly.  He apparently wants to make sure there is no confusion for his readers as to the purpose of his writing.

He wrote:

• So that the joy of those who had seen Jesus may be complete (1:4).
• That his readers may not sin (2:1).
• Because his readers’ sins are forgiven in Christ (2:12).
• Because fathers know God, young men are strong and have overcome the evil one, and children know the Father (2:13-14).
• Because his readers know the truth (2:21).
• So that his readers understand those who are trying to deceive them (2:26).
• So that those who believe in Christ will know they have eternal life (5:13).

Themes of God
John identifies two major characteristics of God and uses them to make up two main themes throughout the book.  God is light (1:5) and God is love (4:8).  Those who walk in the light are of God.  Those who walk in darkness are not of God (1:6-7).  We walk in the light when we obey God’s commandments.  Those who love God love others.  Those who do not love others cannot claim to love God (4:20-21).  If God is love and we claim to abide in Him, then we must be characterized by love.

Fellowship
Underlying the themes and messages of the book is the idea of fellowship.  John says in the introduction that the purpose of his and the other apostles’ sharing of the gospel is so that his readers can have fellowship with them and ultimately with the Father and the Son (1:3).  Fellowship is a wonderful word when it is applied to our relationship with our Creator.

Fellowship (koinonia) is a personal experience of sharing something significant in common with others. It’s the pleasure of being in a group when you see eye to eye on what really matters. It’s having similar values and responding with the same kind of affections to what really counts.  So to say you have fellowship with the Father and His Son means that you have come to share their values. You believe what they believe and love what they love. And so you delight to spend time together. You love to include them in all that you do. You cherish the thought of spending an eternity getting to know them better.  (John Piper, Eternal Life Has Appeared in Christ; Sermon on I John 1:1-4; January 27, 1985.)