Proverbs 14:33 "Wisdom resteth in the heart of him that hath understanding: but that which is in the midst of fools is made known."
Wisdom and understanding go hand in hand. The fear of the Lord is wisdom, and the fear of the Lord is to hate evil. Understanding is knowing then what God hates and departing from it (Job 28:28, Prov. 8:13). The fool continues in his sin and does not take sin seriously. He knows it is dangerous but does it anyway and does not consider or care what the consequences are. His actions are a display of what is in his heart, and the treasure of his heart is certainly not wisdom (Prov. 14:9).
Now lets apply it. What rests in my heart? It is interesting to note that wisdom begins in my heart just as sin begins in my heart. I have the choice to act on wrong thoughts or to be wise and take those wrong thoughts captive in obedience to Christ. As a Christian, my heart ought to exude the love of God and His hatred of sin (Rom. 12:9). Does it? Or, do I find pleasure in sin? I ultimately choose what will rest in my heart, wisdom or selfish pride. Which of these two am I giving a resting place in my heart?