They have closed their fattened heart. with their mouth they speak arrogantly.
David describes people whose heart has grown hard from self-satisfaction and evil desires. The phrase “they have closed their fat heart” points to an inner condition in which a person becomes so accustomed to his desires, strength, or prosperity that he is no longer sensitive either toward God or toward the pain of others. Such a heart is corrected with difficulty, because it feels satisfied and secure in itself. That inner pride is immediately seen also in their speech: “with their mouth they speak arrogantly.” A person’s tongue often reveals what has already been established in the heart. When self-sufficiency and arrogance rule within, speech becomes haughty, harsh, and demeaning to others. The verse urges the believer to be careful not only about arrogant speech, but also about the condition of the heart from which that speech is born. A person may appear secure and successful outwardly, yet inwardly gradually become hardened. Therefore it is necessary to keep a humble heart, remain sensitive to the pain of others, and remember that every good thing is from the Lord.