If we say that we have no sin, we deceive ourselves, and the truth is not in us.
In the opening few words of his letter, John states clearly certain facts about Jesus Christ that are basic to Christianity. Jesus Christ is the eternal God and he became a real man whom John and his fellow apostles have seen, heard and touched (1:1-2). John’s joy will be complete if he knows that he and his readers share together in the eternal life that comes to them through Jesus Christ. This life unites them to one another as well as to the Father and the Son (3-4).God is light, meaning that he is holy, true, pure and glorious. As darkness cannot exist with light, so sinful things can have no partnership with God (5). This means that although the life God gives believers is eternal, the fellowship that believers have with him can be broken because of sin. In three short sections John gives different advice to various people, to remind them of what is required if they are to have cleansing from sin and fellowship with God.First, if people think they can sin as they please and still have fellowship with God, they are mistaken. But if they are careful to live righteously, they will enjoy unbroken fellowship with God and his people. God sees that they are living as he wants them to, and he graciously forgives those sins that they commit unknowingly (6-7).Second, if people forget that they have a sinful nature and think that everything they do is right, they deceive themselves. But if, after honestly examining themselves, they become aware of their sins, they should confess those sins. God gives his assurance that he will forgive them and cleanse them (8-9).Third, if people claim they never sin at all, they are really saying that God is a liar, because he has declared all people to be sinful. They must allow the light of God’s truth to shine into their hearts and show them what they really are (10).John is not saying all this so that people might think that sinning is normal behaviour for Christians, as if it does not matter if they sin. On the contrary he wants them not to sin. But it is inevitable that they will sin sometimes, and he wants them to be assured that when that happens, cleansing is available because of the atoning blood of Christ. On the basis of his death, Christ can ask the Father to forgive the sinner (2:1-2).