This prayer is such a comfort to me, because I know how often my motivations are screwy. People look at the outward appearance: They see me going to church, posting Bible verses on my Facebook status, writing blogs about Jesus, and the like. But God looks at my heart; He knows when my actions spring from the self-centered desire to feel better about myself or impress people rather than from his Spirit.
That's why I love this verse so much. It's like my reset button. When I feel like my focus has gone off-kilter, I pray these words. It's the only way I know how to set myself straight--crying out for help from my Father.
I can't purify my motivations on my own. Truth be told, most of the time I can't even sort out my motivations on my own. My thought process goes something like this: Wait. Why do you really want to do this? Because God told you to? Or do you just want people to think you're doing something great for the Kingdom of God? Maybe He's called you to do something "behind the scenes" to keep you from becoming prideful. Or is that just an excuse you're using because you're afraid?
I usually continue in this line of thinking until I am utterly frustrated and confused, and eventually it occurs to me that I'm getting nowhere. That's when I realize (again) that I can't fix the inner-workings of my heart on my own. My only hope is to rely on God's mercy. Create in me a pure heart, O God.
Then the relief comes. The problem is out of my hands. The thoughts ping-ponging through my brain go quiet. The muck hidden in the deepest places of my heart is washed away. And I am at peace.