There is an often-ignored reality that the human heart is a lying, wicked thing. We think that we are doing the right thing and feel so proud of what we have done only to realize that our motivation; our heart was not right and so all the work was for naught. But, if I cannot even know my own heart, what hope is there of me knowing the heart of others and being able to determine why they are doing what they are doing? The short answer is: I cannot.
It is enough for me to examine myself. The Bible tells me, frequently, to do as much. Scripture often tells the believer to examine him- or herself and to check our motives. I am not told to examine others’ hearts. And this deceitfulness; this sickness noted by Jeremiah may very well be the cause. The question Who can know it? is abundantly valid. I am incapable of plumbing the depths of the human heart. There are depths of wickedness of which humankind is capable that baffle me. Likewise there are depths of kindness of which the human heart is capable that rock me to my core.
We, believers, need to be careful not to judge the hearts of others. We may be correct, but hearts are deceitful and desperately sick. We may have been lied to by any and all hearts — including our own. The human heart needs the Great Physician, Jesus Christ to apply the salve of His blood and cure it. I need that salve applied daily; hourly; in a constant flow until such time as my heart beats in time with His.