Proverbs 4:23 "Above all else, guard your heart, for it is the wellspring of life."
Our attitudes, motives, thoughts, actions, reactions, and everything else come from our hearts.
We MUST guard our hearts which means in part we watch carefully. We watch carefully and take note of what proceeds from them----because what proceeds from them can truly give indications as to where we are sinning or not submitted in obedience to the Lord. But we not only place careful watch over what proceeds from them. We are also careful about what we allow to "take root" in them---we are discerning of truth versus error. We consider our heart valuable and protect it by not choosing to believe lies or falsehood.
Our hearts are the wellspring of life within and everything flows from them.
Lord, help me to continually, intentionally, and actively guard my heart.