Written for assurance of salvation

Have you ever heard that you should read St. John's first epistle to see whether you pass its tests of evidence that you have been born again? Those who teach it as a list of tests overlook the many passages in the letter in which the Elder affirms the faith of the baptized congregation reading his letter (or hearing it read). For three examples, he says, "you have overcome the world," "you know all things," and "greater is he who is in you than he was in the world." Take comfort in those promises to you, and read the letter again, looking for similar unconditional promises. They teach the gospel, the good news that you are forgiven because Christ took away the sins of the whole world, including all of your sins. There is no judgment and no fear in that message. "Perfect love casts out fear."
In order to further encourage the faith/assurance of those reading this letter, he warns them against the false teachers, the "antichrists," who say they know God without any concern for his children and who even deny that God came in the flesh to save us from our sins. Those warnings may also be applied to those who are not alarmed by their sins, including those who trust in their decision and in a false doctrine of eternal security rather than in Christ alone. To them, no good news of forgiveness should be offered but only the condemnation of God's law. Until they recognize that his law condemns their lawless works, they will not believe the gospel. Before they can receive the cure, they must recognize that they are sick.
In short, law's message of judgment is for us when we do not lament our sins. Once we are terrified by God's proclamation of judgment against us, the law has served its purpose and should be set aside to make way for the gospel, God's free promise of forgiveness.
Many false teachers take a very different approach, either by wielding the law against those who already feel its condemnation or by proclaiming the gospel to those who sense no need for forgiveness. Other false teachers mix law and gospel in a way that softens the condemnation of the law or takes away from the comfort of the gospel, against which there is no law. There still many antichrists.
Even as baptized Christians, we daily need both God's law and his gospel. Since we sin daily, daily need to hear God's judgment against our sins, to repent, and to believe the good news that we are forgiven freely. Once our heart, hearing the law, condemns us, we should take comfort in the promise of the gospel that "God is greater than our heart and knows all things" (1 John 3:20). Then our heart will not condemn us, and we will have the assurance that he hears and answers our prayers (1 John 3:21-22). That faith will be active in works of love for our brother. Later, we again become secure in our sins, and God will again proclaim his word to us: first the law, and then the gospel. The process will continue until Christ returns and we see him as he is.
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