The spiritual desire for happiness, when it is inspired and guided by the Word of God, sets us upon a long journey marked by various trials, which progressibely purify our hearts in regard to our principal instincts. … Scripture compares this to the workof dyeing cloth or the purifying of gold and silver, and the Fatehrs well understood how the Beatitudes combine to effect the cleanness of heart needed for seeing God and sharing his bliss. When in the end it is purified, the desire for happiness will have changed its nature, so to speak; it will spring henceforth from charity, which God alone can form.

Pinckaers, The Sources of Christian Ethics