The cry of the psalmist in Psalms 51:10 is the shout of someone who recognizes: alone I can't. He doesn't try to fix himself first to then seek God; he goes straight to the Source and pleads: "Create in me a pure heart."
This reveals that purity is not just the result of discipline or human goodwill, but of a supernatural work that God Himself performs in us. There is something that only He can do in the depths of our being, far beyond what any personal effort can achieve.
Just like David, we also realize that our heart easily gets lost, becomes contaminated, strays, and leans towards what distances us from God. At some point, we discover that it is not enough to try to be better: we bump into the limits of our own nature and realize that something inside us no longer works as it should.
It is precisely there that we understand our real need: not just for superficial adjustments, but for a heart renewed by God. And the good news is that the same God who heard David's cry is still ready today to hear your request, to answer your prayer, and to begin in you this work of inner transformation.