First John is a general epistle written to Christians so that believers may know that they have eternal life (1 John 5:13). In this letter, spiritual truths are narrated in simple sentences. This is a practical letter in which the moral and practical applications of the Gospel are explained. The writer begins the letter by affirming the fact that God is light. Those who want fellowship with God must walk in light and not in darkness. God is love and the source of eternal life. Since Christians are the children of God, they must walk in love. If we do not love, we do not know God.  Love is more than just words, it is action. Biblical love is more than emotion, unconditional in its nature and it is sacrificial giving  and not getting.  Spiritual life begins with new birth.  Jesus Christ is the embodiment of truth. God is light and those who fellowship with Him we must walk in light and not in darkness. Fellowship is the main theme of this letter. John explains the source, purpose, requirements, tests, maintenance and enemies of fellowship in this epistle. 

Authorship
This letter does not mention who wrote it. But there is enough internal and external evidence to conclude that this letter was written by the writer of John’s Gospel and Revelation. The thought and vocabulary such as new commandment, eternal life, Savior of the world and works of the devil coincide with the John’s Gospel. There was a general agreement in the early church that this epistle was authored by John the apostle from Ephesus between A.D 80-90.

Background: 
At that time the church was facing the crisis of the false teaching called Gnosticism. This sect professed to be Christians but claimed that they are enlightened people and have additional knowledge than what the apostles taught. The Gnostics took pride in their knowledge and thought that their ideas are better than the historical account of Christ. They spiritualized the literal incarnation and resurrection of Christ.  They thought that they are myths and they have only spiritual meanings. They taught that they are saved by grace so that they can do whatever they feel good in their body.  According to them matter is evil and not created by God.  Only our soul is pure. So it is unthinkable that God became flesh and dwelt among us. They denied the incarnation and deity of Christ. In this letter John concludes that "Gnostics" are not Christians and warns believers against the danger of following these false teachings. John teaches that we can know God only through Jesus Christ (John 1:18; 14:7).  Christ alone is the embodiment of life, light, love and truth.  John wrote his epistle to encourage Christians to remain in truth, purity and love as they wait for the appearance of Christ.
​