First John is a general epistle written to Christians. It was written so that believers may know that they have eternal life
(1 John 5:13). In this letter, deep 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. 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 word, it is action. Biblical love is unconditional in its nature and is more than emotion. It is sacrificial giving and not getting. Those who fellowship with God must possess divine life. Spiritual life begins with new birth. God is truthful. Jesus Christ is the embodiment of truth. God is light. Therefore, to fellowship with Him we must walk in light and not is darkness. Fellowship is the main theme of this letter. The writer explains the source, purpose, requirements, tests, maintenance and enemies of fellowship. The writer encourages Christian fellowship in this epistle.
The writer of 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, works of the devil and take away the sins 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.
At that time the church was facing the crisis of the false teaching called Gnosticism. This sect professed to be Christians. They have claimed that they are the enlightened people and have additional knowledge, superior to what the apostles taught. The Gnostics took pride in their knowledge and taught that ideas are greater than historical facts. They taught that literal incarnation and resurrection of Christ 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. Matter is evil and not created by God. 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 warned believers against the danger of their false teachings. John teaches that we can know God through Jesus Christ. He is the embodiment of life, light, love and truth.