John finishes his letter summarizing the truths he has presented throughout and exhorting believers to keep themselves from idols
John gives believers assurance of eternal life, relationship with God, and perseverance
The Father has testified that His Son is all that is needed for eternal life. The True Jesus has come by water and blood.
John demonstrates the reality of the believer's salvation and the assurance of that salvation
God is Love, therefore if God dwells in us, we will love
John gives doctrine and the Spirit as evidence of salvation
John gives believers assurance of his perfect word in salvation
John gives the love of the brethren as an evidence of salvation
John gives the evidence of having been adopted
John assures the believer that he needs nothing "extra" from God. Believers have everything in the gospel.
John identifies those seducers who were attempting to lead the believers into error. He calls them antichrists and gives us characteristics so that we can identify who they are. When we know who is "anti" Christ, we have a test by which we can discern those who seek to lead us astray.
John explains the love God hates and shows the dangers of falling into the love of the world. A life of loving the world is also evidence that one does not have fellowship with the Father
John takes an aside to assure believers of their standing before Christ
John here gives the believers the test of love as a measure of Christian authenticity. The test is measuring God's work in His children, not how well His children are performing. Believers love the brethren.
John describes the believer's advocate with the Father. Jesus is our propitiation. The evidence that he is our advocate is the new life he produces in us.