....this person speaks truth in his heart. A curious turn of phrase. It is not enough to speak truth with one’s mouth. Not only is there always the question of just what the truth is, and when it might be appropriate to withhold some part of it, but the more serious problem is that truth-telling can become crass or calculating when it loses its moorings in the character of the truth-teller. Hence the harder task of telling truth to oneself. Such honest is a prerequisite of integrity.
Mark Hamilton, discussing Psalm 24