My heart is at peace when I want what God wants, when I desire only what He desires. . .My mind is at peace when I know what God knows insofar as a creature can participate in the ocean of divine wisdom. My mind is at peace when I assent because I want to do whatever God has revealed. Not because I understand what this means or can explain the mysteries of revelation, but because I trust in God’s authority and submit my intellect to His. In a word, I have peace of mind when I have the truth; when my thoughts agree with God’s thoughts, and my judgments correspond to His, I have the truth and I am at peace. Peace of mind, then, is the experience of the truth. It is the result of truth. It is the fruit of truth.
– Father John Hardon