Psalm 17:10 - "They close their hearts to pity; with their mouths they speak arrogantly."
Let me make four observations concerning this verse. First, consider the somberness of this verse. It says, "They close their hearts...". They do this themselves. We do this to ourselves. Our hands and our hearts labor to do this.
Often when our sinful heart is exposed we blame our circumstances or other people. We blame the other people's kids for the troubles our kids are now in. We say that the system is to blame. But scripture says here that we close our hearts. And having hardened our hearts all other things are effected correspondingly.
Secondly, we see the progression were in. We are capable of becoming more and more hardened with time. James speaks of sin progressing all the way to death if left alone (James 1:15).
The Puritan Richard Baxter says, "One degree (of sin) prepares the heart to another, and one sin inclines the heart to more...A spark is the beginning of a flame; and a small disease may bring a greater."
On the positive side, Peter speaks of the growth of the saint in sanctification. We are to progress day by day in the varied graces of God. 2Peter 1:3-11
Thirdly, a heart that is full will speak and act to reveal its nature. To have a closed heart does not mean that it is an empty heart. On the contrary, it is full of envy, bitterness, malice, wrath etc. (Eph4:31)
Neither does a closed heart mean that it can't be calculating. Such a person 'surrounds' his prey. He is like a 'young lion waiting to ambush'. (11-12). A hard heart is a devising, calculating and cunning evil.
Observation four - a crooked heart leads to crooked actions and speech. Look at Psalm 17:11, "They have now surrounded our steps; they set their eyes to cast us to the ground." Do you see how a crooked heart is reflected in the actions? They encircle them to do harm. A Christian ought not be this way. Instead they are to follow Christ straight to glory with Christ at the head (Psalm 16:8).