"The heart is deceitful above all things!" This is such a profound and countercultural statement. It's also one of the many reasons why I hate the vapid, and all too common, excuse for unjustifiable behavior: "the heart wants what the heart wants." Blech!
Moar C.S. Lewis! Prayer isn't an obligation in this case, and it serves not only God (presumably why we pray), but is also beneficial to the individual praying. Lewis recognizes both parties in the relationship and how important both God and human beings