“My little children, these things I write to you, so that you may not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous” (1 John 2:1).
The Apostle John writes a message of joy as he pens this epistle to those fellow disciples toward whom he feels a loving, familial relationship. He has just completed his description of human nature, saying sin will happen, even with the most careful.
Those who receive this epistle hear John firmly teach that they are not to sin: but he immediately provides the remedy when they do commit a sin: that remedy is Jesus Christ, the One who champions our cause before the Father. That is the “joy” of this message.
This passage presents no dilemma for Christians of any age. John is saying that those who are sincere in their obedience of the gospel have given up sin as a way of life and they have no desire to return to it. Temptations do come, however; and since we are human, we sometimes fall short of our commitment.
When we do, Jesus, by His sacrifice on the cross, has made possible our return to a faithful position with the Father. According to other passages, that reuniting can happen as soon as we repent, confess our sins, and ask for forgiveness.