1 John

Much of this 1st epistle of John echos things that were written in his gospel, including the first verse, which speaks of Jesus as being the Word of Life from the beginning (see John 1:1).  This is a general epistle, which was meant to be circulated around to the various churches, and it is clearly a companion to the gospel of John.  The gospel of John was written to prove that Jesus is the Christ, Who was God sent from God the Father, so that people might believe and be saved.  This epistle expands on that theme, emphasizing that The Christ is Jesus, and providing practical instruction for Christian living.

We are instructed not to sin against God, but that when we do sin, He will forgive and cleanse us when we repent and seek His forgiveness in Christ.  Those who are saved are living in the light of God, Who is Jesus Christ, and those who hate their brothers or sisters in this world demonstrate that they remain in darkness.  Love is the key to life in Christ, as we cannot claim to belong to God if we do not love others, just like Jesus first loved us.