There are two passages from the Book of Jeremiah that are side by side, but seldom preached together. Each is used as a separate text for sermon-making.
[Jer 17:7-10 ESV] 7 “Blessed is the man who trusts in the LORD, whose trust is the LORD. 8 He is like a tree planted by water, that sends out its roots by the stream, and does not fear when heat comes, for its leaves remain green, and is not anxious in the year of drought, for it does not cease to bear fruit.” 9 The heart is deceitful above all things, and desperately sick; who can understand it? 10 “I the LORD search the heart and test the mind, to give every man according to his ways, according to the fruit of his deeds.”
The most often used verse is v. 9 about the deceitful heart. The one about trusting the Lord comes in as a close second in familiarity.
Trusting in the Lord with the blessing attached can be very encouraging to hear. But then, the preacher turns around the next Sunday and tells his flock that they cannot trust their heart because it is wicked and will only lead them into evil and away from God.
However, these two couplets should be considered together, since that is how they are used by Jeremiah.
With the focus on v. 9, which ends as a question, the answer given in v. 10 is often ignored. Who can know and understand the heart? We are assured that we are not able to do so due to its deceitfulness.
Jeremiah reminds us, though, that there is one greater than our heart—the Lord.
That final statement takes us right back to v. 7, which tells us to trust the Lord.
We are to trust the Lord and not our own heart, mind, or thinking, because it is deceitful.
Is it? Really?
How important might it be to know the rest of the story?
Jeremiah later writes what God says—I will give them a heart to know that I am the LORD, and they shall be my people and I will be their God, for they shall return to me with their whole heart. (Jer. 24:7)
I will give them one heart and one way, that they may fear me forever, for their own good and the good of their children after them. (Jer. 32:29)
The Lord knows the heart of man, that it will continually turn away unless some kind of surgery is done to correct its malfunction.
That surgery has been done through Jesus Christ.