Sinclair Ferguson reminds us that piety not marinated in the gospel will run out of gas-that imperatives minus indicatives equal impossibilities:

The first thing to remember is that we must never separate the benefits (regeneration, justification, sanctification) from the Benefactor (Jesus Christ). The Christians who are most focused on their own spirituality may give the impression of being the most spiritual … but from the New Testament's point of view, those who have almost forgotten about their own spirituality because their focus is so exclusively on their union with Jesus Christ and what He has accomplished are those who are growing and exhibiting fruitfulness. Historically speaking, whenever the piety of a particular group is focused on OUR spirituality that piety will eventually exhaust itself on its own resources. Only where our piety forgets about us and focuses on Jesus Christ will our piety nourished by the ongoing resources the Spirit brings to us from the source of all true piety, our Lord Jesus Christ.

Sinclair reminds us that the secret of gospel-based sanctification is that we actually perform better as we grow in our understanding that our relationship with God is based on Christ's performance for us, not our performance for him. In fact, those who end up getting better are those who increasingly realize that their relationship to God does not depend on them getting better. This means, as I said in a post a couple weeks ago, that Christian growth does not happen first by behaving better, but believing better-believing in bigger, deeper, brighter ways what Christ has already secured for sinners.