"The heart is deceitful above all things, and desperately wicked" (Jeremiah 17:9)
Over the years we've tried our hand at raising a few backyard animals---(chickens, geese, etc). One of my customs is to save food scraps in a few 5-gallon buckets. I use these to feed the scraps to the animals, or to store them to eventually throw on the compost pile.
Yet for the past several months I've also been busy finishing off our basement. I've accumulated a lot more buckets---paint, drywall mud, primer. Somehow, in the confusion of all these projects, one of the food buckets ended up in the contstruction supplies. All was well and good--at least until I opened it in the house. The smell of that bucket--now containing several months worth of rotted food--immediately filled the house.
That food bucket is something like the human heart. All might look well and good on the outside, but on the inside it is horribly rotten. C.H. Spurgeon captured the true condition of our hearts when he wrote the following:
"There is nothing one half so worthy of abhorrence as the human heart. God spares all eyes but His own that awful sight, a human heart; and could you and I but see our heart, we should be driven mad, so horrible would be the sight."
Jeremiah 17:9 isn't just talking about our evil deeds. It is highlighting the general condition of our heart apart from Christ. Of course, this does mean that we are prone towards evil thoughts and deeds. But it also means that even the "good" things we do are considered evil in the eyes of the Lord. Isaiah 64:6 tells us "all our righteous acts are like filthy rags". Everything is rotten, down to our very core.
The Christian does not stand before God because he or she has achieved some degree of righteousness by having lived a good life. The true Christian, instead, is one who recognizes he or she is a rebel and villian--but one who has been redeemed and changed by Christ. With David, we cry out "create in me a pure heart, O God" (Psalm 51:10).