We recently noted an ongoing discussion about the effort we’re called to make in our sanctification. I believe Scripture tells us that although we can do things that look like sanctification, if those actions are done in the flesh they are simply behavior modification. It’s a change in the heart that is desired, not simply an outward change in actions.
I’m currently reading The Spirit-Filled Church: Finding Your Place in God’s Purpose, by Terry Virgo. Virgo takes this argument one step further, showing us that using the law for sanctification gives Satan the opportunity to heap condemnation on us. “The law always kills in the end,” Virgo notes.
This portion of The Spirit-Filled Church (available for pre-order at Amazon and via Amazon in the U.K. here or worldwide from the U.K here) outlines Virgo’s case. It’s in agreement with what we’re advocating in our current Completed by the Spirit series:
It is essential for us constantly to recognize our death to law. It is no longer the basis for our relationship with God and never will be. We are married to Christ and our fulfilment as Christians is bound up in our love relationship with him.
All evangelicals know that they can never be justified by the law, but what they often fail to realize is that they cannot be sanctified by it either. The law always condemns. Its purpose is to bring us to Christ (). The tragedy for many believers is that they get caught in a trap. They reach a crisis when they feel deeply challenged by a word from God concerning their sanctification and they deplore their recent history. With new-found zeal they determine to do better in the future. But at that very moment they make the fatal error that will lead them to certain failure and distress. At the time when they most need to break the snare, they choose the wrong choice. They begin to impose certain laws upon themselves in order to help them reign in life. They perhaps adjust their alarm clock for half an hour earlier. They determine to read the whole Bible in the coming year, and so on. These steps may have real worth in and of themselves, but they do not provide us with the keys to “reign in life”. The mistake is in thinking that in order to reign in life we must do something, while the New Testament does not teach that. It says that we reign in life by receiving the abundance of grace and the free gift of righteousness ().
The problem for many Christians is that they always feel condemned. But the answer to condemnation is never simply to improve our performance. It is to reckon on our position through grace. God has justified us freely as a gift. Condemnation is to do with guilt, not with feelings or improved performance. If we, through grace, are declared “not guilty” by God, then we cannot be condemned. Only the guilty man stands condemned. It is God who justifies, and if God has declared us “not guilty”, Satan cannot take us to a higher court. There is none. There is no condemnation for us, not because we have been doing well lately, or because we have set ourselves a new standard, but because we are in Christ Jesus. He has carried our guilt on the cross. The more we come to enjoy that truth, the more we will know how to refuse Satan’s constant barrage of accusations aimed at getting us down.
If Satan can get us off our ground in Christ Jesus and onto the ground of our effort, he knows he has us in our grip. We may succeed for a while with New Year resolutions but even before the chill winds of February, condemnation looms large all over again. The law always kills in the end. 
 Virgo, Terry. The Spirit-Filled Church: Finding Your Place in God’s Purpose. Grand Rapids, MI: Monarch, 2011. Print. p. 59–60.
2 Let me ask you only this: Did you receive the Spirit by works of the law or by hearing with faith? 3 Are you so foolish? Having begun by the Spirit, are you now being perfected by the flesh? (ESV)
24 So then, the law was our guardian until Christ came, in order that we might be justified by faith. (ESV)
17 For if, because of one man’s trespass, death reigned through that one man, much more will those who receive the abundance of grace and the free gift of righteousness reign in life through the one man Jesus Christ. (ESV)