What is the Gospel for?

Many times, to many of us, the Gospel is synonymous with evangelism.  We'd say, "Preach the Gospel so people can be saved!"  but in reality, that's a very shortsighted view of the Gospel.  It's not only has the power to save, but it's also the same power that changes us on a daily basis - sanctifies us, conforms us to the image of Christ.  I've heard John Piper say once before (loosely quoted): You don't get saved by the Gospel, and then go about becoming holy under your own power, or by some special plan.  You don't get saved, and then move on to the real meat.  We are to be dependent on it from conversion to death.  He references Paul's correction of the Galatians in Gal 3:3-5:

Are you so foolish? Having begun by the Spirit, are you now being perfected by the flesh? Did you suffer so many things in vain—if indeed it was in vain? So then, does He who provides you with the Spirit and works miracles among you, do it by the works of the Law, or by hearing with faith?

(Updated:
And so what we should be saying is, "Please, preach the Gospel, because my soul and spirit need it always!"  It is the reminder of God's glory and His work in us.)

Below is an excerpt from a post by Tim Challies on his blog where he discusses the same thing with better words.  You can read his entire post, titled "The Heart's Position", here.

I have written often of those authors and pastors who encourage Christians to preach the gospel to themselves every day. I see some of the value of doing this, though my practice of it is too sporadic. What such teachers want us to see is that the gospel is not merely the gateway to the Christian life, but the fuel of the Christian life. What they want us to understand is that the gospel is not simply defensive, the thing we turn to when we have sinned and are eager for some assurance of pardon. Rather, the gospel puts us on the offensive against sin and toward holiness. We ought to continually bring the gospel into our hearts and minds as a means of spurring ourselves to greater love for God which in turn generates a greater desire for obedience to him.

And here he explains how he "preaches the Gospel to himself": 

...As I turn to the Bible to read the predictions and prophecies of the coming Messiah, as I consider the narratives of Christ’s birth, life, death and resurrection, as I ponder the epistles where all of these things are explained and illuminated, as I consider the day of Christ’s return, my love for God and my trust in him must necessarily increase and thrive. As my love swells, so will my desire to do those things that honor him and bring him glory.

...And what has he promised to do? He has promised to make me holy. He has promised to sanctify me, to help me put sin to death and to replace it with joyful obedience. He has promised that the Holy Spirit is operating within my life to bring me into closer conformity with Jesus Christ. He has promised that the very same power that has saved me is now sanctifying me. Now I have hope and confidence that this really is happening and that this really can happen. I really can put sin to death, I really can grow in holiness, I really can grow in Christ-like character and look more and more like the One who saved me.

I simply cannot trust that all of this is happening and that all of this will continue to happen if I have no ability to trust in what has already been accomplished. However, when I trust God for what he has done, now my heart is properly positioned to trust God for all that he has promised to do. And, therefore, the gospel must be my joy and meditation every day.