John writes the wonderful promise, "If we confess our sins, God is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness." (1John 1:9)
The first thing you'll notice about the promise is that a commandment is attached to it, and we must keep the commandment if we want the promised blessing. If we obey the commandment to confess our sins, all our sins will be forgiven and cleansed.
This promise is not unique —or even unusual— among the promises of God. In fact, most of God's promises have commandments attached. It is rare for God to make an unconditional promise —like the rainbow promise for example (Genesis 9:8-17)— requiring nothing of those to whom it is made. The promised blessings of knowing God and having fellowship with him come with commandments to keep. "The one who says “I have come to know God” yet does not keep his commandments is a liar and the truth is not in him" (1John 2:3-6).
Now on its face value, the promise seems to be saying that any sin you confess, God will forgive. But on the other hand it seems to imply that any sin you fail to confess God won't forgive! Now that presents a problem. It would seem to make the blessing of full forgiveness dependent upon one's perfect performance in remembering and confessing all one's sins —every single one!
That would very likely leave us condemned, and not counted righteous, because we didn't get the confession of our sins 100% right. This is the principle that "whoever keeps the whole law yet stumbles in one point, has become guilty of all" (James 2:10).
Now we cannot answer this problem with a "soft God" approach, because God's love is never indulgent —it's tough love. Paul says, "work out your salvation with fear and trembling" and "prove yourselves blameless and innocent" (Philippians 2:12-15) —not 80% blameless and innocent. God's standard is exacting. "God is light and in him there is no darkness at all" and we must "walk in the light as he himself is in the light" —no less a standard will do (1John 1:5-7). That's the problem.
If you go before a judge, you usually have a qualified barrister to put your case for you —because the law court is so exacting. John says, "If we sin, we have an Advocate with the Father, Jesus Christ the righteous" (1John 2:1-2). We ought to make our confession of sins only through the priest God has appointed and anointed, namely Christ Jesus (Hebrews 4:14-16, 10:19-23).
Both the Holy Spirit and Christ intercede for us when we pray (Romans 8:26-27,34). So, although our very best efforts at confession may be far from perfect, our confession will be perfected by divine intercession —which demonstrates our reliance upon the perfection and authority of our High Priest and his Holy Spirit. This intercession meets God’s exacting standards on our behalf.
This solution is most wonderful. There's a danger, however, that we might think we don't have to concern ourselves with the problem of sin, or we don't need to make any effort of our own to overcome and avoid sin. We may even falsely think that we can "continue in sin that grace may abound" (Romans 6:1).
John makes it very clear that the true child of God cannot make a practice of sin but must practise righteousness (1John 3:4-10). Nothing John has previously said should be taken to mean that sin is inevitable or that we can sin with impunity. John in fact states, "I write that you may not sin" (1John 2:1). It is wonderful that, if we sin, we have an Advocate in Jesus Christ. But it is far better that we use the power he gives us to overcome and avoid sin in the first place.
"By one offering, Christ has made perfect forever those who are being made holy" (Hebrews 10:14). This tells us clearly that we are not perfect in ourselves of our own virtue. Rather, we are made perfect by virtue of Christ's spotless sacrifice.
The appropriate response, is not to continue in sin but to do our diligent best to perform the commanments attached to God’s promises. It is Christ who does the perfect work that makes us fit to have fellowship with God. In that grace, John tells us not live sinfully but to walk in the light and confess our sins in order to be cleansed (1John 1:5-10, 2:1-6).
It follows then, that we should not practice sin but practice the truth. That is fitting for us who receive forgiveness of all sins, and are continually cleansed by Christ's blood, through God’s kindness and his just acknowledgement of Christ's perfection on our behalf.
It would not be faithful and just of God to merely pretend our sins didn't happen. It wouldn't be faithful and just of God to make a compromise with evil by letting our sins go unpunished. On the other hand, nor would it be just of God to leave us without a means of forgiveness. So God being loving, kind, gracious, and merciful, found a right way to make forgiveness possible.
The punishment for our sins fell upon Jesus (Isaiah 53:5-6). This enables Christ to successfully intercede for us (Romans 8:34, 1John 1:1-2). So God can make a promise of full forgiveness, and cleanse us from all sin, without any compromise of his perfect standard.
So which is the appropriate response to this grace? Is it, as some teach, to continue wilfully in sin, or is it rather to practice righteousness as best we can? Our response should be...
I myself will do my best while Christ himself does all the rest.