When Jesus asks the blaspheming Pharisees (Matthew 12:24), “How can you speak good when your hearts are evil?”, he means for us to realize that this is impossible.
But don’t fallen, unregenerate men do good? Yes, in one sense, by God’s common grace, on a horizontal plane, men do “good” things, but on a vertical plane and in the most ultimate sense, all of their acts are evil. Consider pirates.
In a gang of pirates we may find many things that are good in themselves. Though they are in wicked rebellion against the laws of the government, they have their own laws and regulations, which they obey strictly. We find among them courage and fidelity, with many other things that will recommend them as pirates. They may do many things, too, which the laws of government require, but they are not done because the government has so required, but in obedience to their own regulations.” – W.D. Smith
As fallen, unregenerate men we are pirates, glory thieves, stealing the glory of God and giving it to other things. All of our life is one of idolatry. All behavior flows from the heart. If our actions are not springing from a heart that treasures Christ supremely, something else is being treasured. In doing “good” we are doing a greater evil. We “keep” other commandments only to break the first one (Exodus 20:2). As fallen men we are never truly good, at best we are subdued. We “obey” only when it is convenient to get what we want, only so that we can live to rebel another day.
Where then do the good trees (hearts) come from that bear good fruit; fruit that will serve as evidence of one’s justification (v. 35, 37)? Answer: Regeneration.
And I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone from your flesh and give you a heart of flesh. And I will put my Spirit within you, and cause you to walk in my statutes and be careful to obey my rules. – Ezekiel 36:26-27
All praise be to Jesus for the good tree that I am and the good fruit I produce.