The Gospel is what saves me and the Gospel is the power and motivation I need to be conformed to the likeness of Christ. If I try to be sanctified by doing Christian disciplines apart from the Gospel I will become (or remain entrenched as) a Pharisee. Paul said he knew that in himself, that is, in his flesh, nothing good dwelt. Jesus said "Apart from Me, you can do nothing."
We must take care how we build on the foundation that Christ has built. Paul asked the Galatians how they expected to grow as Christians by mere human effort. It is hopeless! Gal. 3:1-3 says:
You foolish Galatians! Who has bewitched you? Before your very eyes Jesus Christ was clearly portrayed as crucified. I would like to learn just one thing from you: Did you receive the Spirit by observing the law, or by believing what you heard? Are you so foolish? After beginning with the Spirit, are you now trying to attain your goal by human effort?So, whatever we do that is not Gospel-motivated, cross-centered, and done out of faith, trust, reliance, submission and dependence on God, is worthless. I can do Christian disciplines all day long and be the most obedient person on the face of the earth. If I'm not filled with, reliant on, submitted to, and trusting God for every bit of it, it will be junk. All my righteouness is filthy rags. Read Tim Keller's treatise - The Centrality of the Gospel, at http://www.redeemer2.com/resources/papers/centrality.pdf