"The only man who has the right to say that he is justified by grace alone is the man who has left all to follow Christ."- Bonhoeffer, The Cost of Discipleship
I read this quote in the book I'm currently reading, Don't Waste Your Life by John Piper, which I would highly recommend. You can download and read FOR FREE. You can read any John Piper book for free at his website. Here's Don't Waste Your Life:
But be warned, it will probably make you evaluate all of your selfish motivations for any of your life/career pursuits.