Indeed. It must be by the Spirit of God. If it is done any other way, it won't be real. Reminds me of the story about Ben Franklin. He used to keep a little book where he recorded how he was doing on certain virtues that he felt important. After a while, he noticed that he was getting proud of his accomplishments, so he added another column for humility!
But that's the end result of striving—well either that or despair because you can't attain. It is only by the Spirit living within us that we can truly be holy and good...