Doing Bad vs. Being Bad

This afternoon I was reading in Eugene Peterson's Psalms: Prayers of the Heart.  The Chapter centers around Psalm 51, which is attributed to David following his actions with Bathsheba.

Peterson writes this:

Our experience of sin does not consist in doing some bad things but in being bad. it is a fundamental condition of our existence, not a temporary lapse into error. Praying our sin isn't resolving not to sin anymore; it is discovering what God has resolved to do with us as sinners.

What are your thoughts?

1. We often thing that granting someone forgiveness hinges on their commitment to not hurt us again. If our prayers to God do not hinge on such a condition - and if what Peterson says is true, then this is the case - then why should we only grant forgiveness to people who resolve to not sin again? Is it possible to promise to not sin again?
2. Doesn't grace gain a bigger meaning if what Peterson says is true? God isn't granting us pardon for what we have done - God is working within us to change us.
3. And is this what sanctifying grace means?