John writes these verses to address major problems. John asks his audience to imagine the terrible scenario: Jesus returns in glory and power and instead of welcoming him we are terrified. We "shrink from him in shame" (2:28). The most basic problem this text seeks to answer is that of church people not abiding in Christ and therefore not being prepared for death and the unavoidable meeting with Jesus. God doesn't want you to wake up on the other side of death only to hear Jesus' dreadful words: "I never knew you; depart from me, you workers of lawlessness" (Matt. 7:23).
But there is a second problem John hopes to resolve: God's true children sometimes lack hope that we are in Christ. This is a huge problem. John says, "And everyone who thus hopes in him purifies himself as he is pure" (3:3). Hope is an unparalleled motivator. Doubt and fear do not produce joyful, satisfying, God-honoring obedience; only joyful hope can do that.
God wants us to know that we have a close relationship with Jesus so that we will be hopeful, happy, and holy people. The way John writes about abiding in Christ answers both problems at once.