8 “And I have meditated in the night with my heart”. No slanderous person seeks for snares in his words, in his heart he has meditated. “I babbled.” Behold there is the former babbling. Watch again, that your spirit faint not. I did not, he says, I did not so babble as if it were abroad: in another way now. How now? “I did babble, and did search out my spirit.” If he were searching the earth to find veins of gold, no one would say that he was foolish; nay, many men would call him wise, for desiring to come at gold: how great treasures has a man within, and he digs not! This man was examining his spirit, and was speaking with that same his spirit, and in the very speaking he was babbling. He was questioning himself, was examining himself, was judge over himself. And he continues; “I did search my spirit.” He had to fear lest he should stay within his own spirit: for he had babbled without; and because all his enemies had anticipated watches, he found there sorrow, and his spirit fainted. He that did babble without, lo, now does begin to babble within in safety, where being alone in secret, he is thinking on eternal years....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)