The final chapter ties together faith, love, and obedience. Whoever believes that Jesus is the Christ has been born of God. Whoever loves the Father also loves the child born of him. By this we know that we love the children of God, when we love God and keep his commandments. For this is loving God, that we keep his commandments. His commandments are not grievous. Faith is the victory: whatever is born of God overcomes the world, and the one who overcomes is he who believes that Jesus is the Son of God.
The writer speaks of testimony. Jesus came by water and blood, and the Spirit testifies, because the Spirit is the truth. If we receive the witness of men, the witness of God is greater. The testimony is this: that God gave to us eternal life, and this life is in his Son. He who has the Son has the life. He who doesn’t have God’s Son doesn’t have the life. The purpose of the letter is stated plainly: so that those who believe in the name of the Son of God may know that they have eternal life.
The closing verses give confidence. If we ask anything according to his will, he listens to us, and we know that we have the petitions we have asked of him. Believers should pray for a brother who sins. Three times the writer begins with the words we know. Believers know that whoever is born of God is kept from the evil one, that they are of God, and that the Son of God has come and given them understanding to know him who is true. The last line is a loving warning: Little children, keep yourselves from idols.