John writes to his audience and tells them some very lofty things about their current state:
I am writing to you, little children, because your sins are forgiven on account of his name.
I am writing to you, fathers, because you know him who is from the beginning.
I am writing to you, young people, because you have conquered the evil one.
I write to you, children, because you know the Father.
I write to you, fathers, because you know him who is from the beginning.
I write to you, young people, because you are strong and the word of God abides in you, and you have overcome the evil one (1 John 2.12-4).
Of course, John tells us I am writing these things to you so that you may not sin (2.1), so he must think that telling his audience all these truths about themselves must contribute in some way to their holiness and obedience to Christ. In fact, these words fit nicely with the general paradigm of obedience that John develops, which is obedience as a result of knowledge.
John is clear on numerous occasions: those who know Christ will obey him, whereas those who do not know him will demonstrate this ignorance through their hatred (e.g., 1.5-10; 2.3-6, 9-11). Obedience stems from knowledge and experience of God and Christ, rather than mere volitional compliance with some set of commands. And so it must be a part of Christian life to know these things, too, and it must be that knowing these things contributes in some way to our holiness.
And it isn't difficult to see how! Being told that we are forgiven of our sins frees us from their burden. No longer do our sins and vices characterize our identities; once they are forgiven, we are now free to be different sorts of people than we previously thought. Think of the freedom of the sinful woman from Luke 7.36-50, after being told that her sins are forgiven! No one in the world can tell her that she is good for nothing or a sinner, because the Lord himself has forgiven her and set her free from that.
Likewise, John tells the young people that they have overcome the evil one, and that they are strong. John is very optimistic about the possibility of Christian holiness, and he doesn't betray any sense that the normal Christian life is one marked by moral mediocrity and consistent shortcoming and failure. No, on the contrary: Christian life is obedience to Christ's commands, and love for our brothers and sisters!
Now I don't know how many of us can say of our own lives that John's words adequately characterize them. I don't think "You have overcome the evil one!" is always the way I feel about my own life. And yet John insists to tell me that this is true, and he is convinced that my understanding this contributes to my own holiness and obedience to God. How to understand this?
I think many Christians are like children who have been told their whole life that they are stupid or good for nothing, even though quite the opposite is true. Such a person, no matter how much potential and value others will see in him, will forever be convinced that he's not smart or that he's not capable of anything. Or consider the case of a girl who is convinced she is ugly when she's not. A whole life can be ruined and paralyzed because a person doesn't know the truth about herself!
In the same way, I take it that we ought to encourage one another with these words (1 Thess 4.18). To convince a person who's sure he's stupid that he's actually quite intelligent takes commitment and friendship and kindness. In the same way, in the context of our churches, we ought to be committed to reminding one another all the time that our lives are to be characterized like this: you are strong! the word of God abides in you! you have overcome the evil one!