Psalm 17:3 Thou hast proved mine heart; thou hast visited me in the night; thou has tried me, and shalt find nothing; I am purposed that my mouth shall not transgress.
Because the Lord searches the thoughts of my heart and tries and tests me, I am motivated not to sin with my mouth. So says David. He purposes not to sin with his words. This is sincere repentance and honest confession. God does not search and test the heart in order to judge and punish, but to bring about repentance and change, to make me a better person. God searches the motivations and movements of the heart out of love for us in order to bring about repentance, faith, and real change. Our loving Lord is not looking to uncover sin so that He can judge and punish us. His purpose is to show us our sin so that we will want to change and determine to do better. Romans 4:2: “God’s kindness is meant to lead you to repentance.”
The Gospel is the power of God unto salvation, and it gives the motivation and ability to purpose in the heart, to want to do better, and to actually change how we talk. The Law tests the heart, convicts of sin, and leads us to the Gospel of Grace. It is because God is kind and good that He shows us our sin and leads us to repent, receive forgiveness, and live a godly life. The Gospel affects our aim and purpose.
We actually invite God to search the heart and test us and find nothing, for Jesus has taken the sin away. However, we are not yet perfected, sin remains in the sinner, and so we continue to need to hear God’s Law and Gospel. It works.