Continuing on with my notes from How To Say No to a Stubborn Habit by Erwin Lutzer:
Chapter 10, The Intercession of Christ and Believers
Christ told Peter, "And the Lord said, Simon, Simon, behold, Satan hath desired to have you, that he may sift you as wheat: But I have prayed for thee, that thy faith fail not: and when thou art converted, strengthen thy brethren. (Luke 22:31-32). Peter did deny Him, as predicted, but without Christ's intercession it could have been even worse or Peter might not have repented or recovered. Plus Christ has been human, felt human needs, been tempted and resisted, so He can empathize with us and in Him we can have victory. "For in that he himself hath suffered being tempted, he is able to succour them that are tempted" (Heb. 2:18). Plus, He is our advocate with the Father (I John 2:1).
Lutzer points out that we're not designed to live the Christian life independently. Various Scriptures (I Cor. 12, for one) illustrate the need for believers to interact with and support each other -- the passages about the church being a body, the promise of prayer where two or three are gathered together in His Name (Matt. 18:20). Though I see and agree with that, I am not so sure I agree with the idea of an "accountability partner." It seems to me that if I am only resisting or undertaking something because I am going to have to report to someone, I am not really doing it as unto the Lord, and it kind of feeds into the performing for the eyes and approval of man. I'd be interested in other thoughts on this.
Lutzer then discusses restoring a believer. When we see a fellow believer sin (not just do something not in line with our preferences, but a clear and actual sin), usually our first impulse is to talk with someone else about it (gossip) or just hope the person comes around, but it is our duty to confront them. According to Matt. 18:15-17 it is to be done privately first, and according to Galatians 6:1 it is to be done in meekness, not self-righteousness.
(Disclaimer: My purpose in jotting down these notes is not to post "the answer" so that people don't have to buy the book: on the contrary, I hope anyone struggling with persistent sin will buy the book. There is so much more there that is so rich. Rather, this is just an exercise for me to review what I have read and studied.)