Repent of good works?

I was listening a message by Tim Keller yesterday, about the parable of the prodigal.
In it he spoke of how we don't just need to repent of our badness, but also need to repent for much of the reasons for our goodness.

We all know that bad/sinful acts ought to be repented of but why would we need repentance concerning good works?
Well, for many of us our good works are tainted:
We do good in order to feel good about how 'good' we are.
We do good in order to earn favour, possibly even salvation with God.
We do good in order to build up a good reputation and make others think we are great.
We do good because it is our duty.

I'm sure you can think of many more reasons why people do good works, but all these are wrong motives.

Good works that actually please God can only done by those who are already His children. We do not work for salvation, rather we work because He has loved us and redeemed us to Himself.
Good works begin with becoming a Christian.
And what of motive?
Surely love is the pure motive for any good work!
We love God and so we display our love through good works.
We love our neighbour and so we want to see thier good and ultimately their salvation and coming to Christ.

Any thoughts?