1 John 1:6 " If we say we have fellowship with him while we walk in darkness, we lie and do not practice the truth. "
This is one verse that always seemed to lend itself to doubting my faith, as opposed to encouraging me in my faith and giving me assurance of my salvation. I think I can directly attribute this to legalism. My understanding of this portion of Scripture would have been that if my obedience is not perfect, then I am in darkness. Ironically, if you read on, this notion is blown away. In verse 8,"If we say we have no sin, we deceive ourselves, and the truth is not in us." In other words, if I somehow manage to deceive myself into thinking I'm no longer sinning at all, then I am actually in the darkness, even if my whole motivation for contriving to believe myself sinless is to find assurance that I am in the light. The only possible way to imagine myself sinless in this way, would be to legalistically devise a law of right and wrong behavior (based on Scripture or not) and then consider myself following this law without error. I have met a few people who have actually done this and claimed to have been literally sinless for several years. I don't think most of us are in danger of this though!
The danger for me is in leaving my faith out of the equation. Living in darkness is something no true believer does. We can't. By this I mean that we cannot go on sinning with no change. That is the way of the world and being born of God changes us forever.
1 John 3:9-10 "No one born of God makes a practice of sinning, for God's seed abides in him, and he cannot keep on sinning because he has been born of God. By this it is evident who are the children of God, and who are the children of the devil: whoever does not practice righteousness is not of God, nor is the one who does not love his brother. "
Why can't we go on sinning? "...for God's seed abides in him..." We have the Holy Spirit living in us at all times if we are truly born of God. It is not possible for us to go on sinning without being convicted and eventually brought to repentance, because in any battle with God, he always wins. If we are able to sin freely without resistance, then we do need to examine whether we are truly born of God, whether the Spirit truly lives in us. ( In my experience, most people who fall into this category of professing christians without any evidence of change, would not actually be able to articulate any personal experience of God's Spirit. In fact, they may even be confused by such questioning.)
Another section of 1 John confirms the idea that living in the light is not referring to literal perfection.
3:2-3 "Beloved, we are God's children now, and what we will be has not yet appeared; but we know that when he appears we shall be like him, because we shall see him as he is. And everyone who thus hopes in him purifies himself as he is pure. "
So what about obedience? I think it's important to understand the role of obedience in our lives. It's essential, but if we get the order wrong it's fatal. Legalism puts obedience first. It becomes the basis of our hope and our faith is directed toward ourselves. God hates legalism because it is pride. True faith in God produces obedience by the power of the Spirit. It is an evidence of our faith and in this way provides assurance that we abide in him. True obedience pleases God because it is in no way connected to our flesh, or own strength. All true obedience proceeds from Christ himself, as a result of being crucified with him, and him living in us. (see Galatians 2:20) (I am not saying that there is no physical labor involved in obedience, I am talking about the spiritual aspect, just to clarify.) So obedience is proof that we have the Holy Spirit in us.
I have been so amazed to discover that far from being a discouraging and condemning book as I once looked at it in my legalism, 1 John is about God's love for us.
4:15-18 "Whoever confesses that Jesus is the Son of God, God abides in him, and he in God. So we have come to know and to believe the love that God has for us. God is love, and whoever abides in love abides in God, and God abides in him. By this is love perfected with us, so that we may have confidence for the day of judgment, because as he is so also are we in this world. There is no fear in love, but perfect love casts out fear. For fear has to do with punishment, and whoever fears has not been perfected in love."
It appears that the key to assurance is abiding in God, so that we really understand and experience his love for us. We have no more fear, because we have no punishment to fear. Hell has been removed from our future and we will stand one day before God with confidence. That can only happen if we are absolutely certain of his love for us. Anyone who places their confidence, or even part of their confidence, anywhere outside of God's love for us (revealed in Christ's work on the cross)is in trouble.
Philippians 3:3, 7-11 "For we are the real circumcision, who worship by the Spirit of God and glory in Christ Jesus and put no confidence in the flesh--though I myself have reason for confidence in the flesh also...But wahtever gain I had, I counted as loss for the sake of Christ. Indeed, I count everything as loss because of the surpassing worth of knowing Christ Jesus my Lord. For his sake I have suffered the loss of all things and count them as rubbish, in order that I may gain Christ and be found in him, not have a righteousness of my own that comes from the law, but that which comes through faith in Christ, the righteousness from God that depends on faith--that I may know him and the power of his resurrection, and may share his sufferings, becoming like him in his death, that by any means possible I may attain the resurrection from the dead."
I think it's clear that there can be no compromise between faith and legalism. It is 'either or" and that's why legalism is very serious, and probably the most dangerous enemy of our faith. What Paul says he gave up was his own rightousness, or claim to God based on anything he did or could ever do. We must all give up this foolish claim, because it can only end in death and eternal punishment, not the resurrection that we all long for.