The First Epistle of John, written by the apostle John, explores the themes of love, fellowship, and the assurance of salvation. John highlights the importance of loving one another, of abiding in Christ, and of living a life characterized by righteousness. He emphasizes the reality of sin, the need for confession and forgiveness, and the confidence believers can have in their relationship with God. 1 John reassures believers of their identity as God's children, calls for genuine love in action, and underscores the centrality of Christ in the believer's life.