Jeremiah wrote one of the most pessimistic assessments of the human heart: “the heart is deceitful above all things and beyond cure. Who can understand it?” (Jer 17:9) But Jeremiah also records how committed God is to renewing our hearts. “I will give them a heart to know I am the Lord … they shall return to me with their whole heart.” Jer 24:7. The promise of the New Covenant (Jeremiah, 31:31-35) is that God will write his law on our hearts.
A surprising contrast. But I think the take-away is we can trust our hearts to God and we need to trust our hearts to God. We can ask him for his help to cure the deceit, and guide our hearts to the place God wants. We can cry out to God with what is in our hearts, because he knows our hearts yet does not reject them.