"Above all else, guard your heart, for everything you do flows from it." (Proverbs 4:23)
A father instructs his son with the teaching his own father gave him: get wisdom, get understanding; do not forget my words or turn away from them. Do not forsake wisdom, and she will protect you; love her, and she will watch over you. The beginning of wisdom is this: get wisdom, and whatever you get, get insight. When you walk your steps will not be hampered; when you run, you will not stumble. Hold on to instruction; do not let it go, guard it well, for it is your life. Do not set foot on the path of the wicked; avoid it, do not travel on it. The path of the righteous is like the morning sun, shining ever brighter till the full light of day. But the way of the wicked is like deep darkness; they do not know what makes them stumble. Above all else, guard your heart, for everything you do flows from it.
The Catechism identifies the heart as the seat of the moral life - the centre from which all human action flows, for good or ill (CCC 2517).
Brothers and sisters, above all else, guard your heart. The battleground of the Christian life is not primarily behaviour but the heart from which behaviour flows. You can modify external behaviour for a season, but if the heart is not transformed, the external change will not hold. Guard what you allow into the heart - what you watch, what you dwell on, what you desire.
Lord God, above all else, guard our hearts. Everything we do flows from them. Be the guardian of what we have not the strength to guard ourselves. Through Christ our Lord. Amen.