Psalm 51:10 Create in me a clean heart, O God, And renew a steadfast spirit within me.
No matter how clean we want to believe that our hearts are, they are not. We have them filled with all manner of sin as we live in this world amongst the sin.
No matter how much we try to mop up dirt or water, we are left with a residue. It is only when we use chemicals or specialist tools that can get things looking clean again.
God is able to do so much more than the chemicals and tools because He can create a new heart within us that no longer attracts the sin we have lived for before.
Nothing can touch your spirit but God!