Purity of Heart
In the consistent Bible view, the heart is nothing less than the taproot of the self, the deep soruce of our character and purposes, of our attitudes and responses, of our self-image and self-projection, in short, of the total human being that each of us is....
Kierkegaard put his finger on the deep truth of the matter when he titled one of his books Purity of the Heart Is to Will One Thing. Jesus spelled out that truth when he said, "You shall love the Lord your God with all your heart and with all your soul and with all your mind. This is the great and first commandment" (Matthew 22:37-38)..Purity of heart is indeed a matter of willing one thing, namely to live every day of one's life loving God.
J.I. PackerPraying: Finding Our Way from Duty to Delight
pp. 38-40