From the Catechism of the Catholic Church:
1718 The Beatitudes respond to the natural desire for happiness. This desire is of divine origin: God has placed it in the human heart in order to draw man to the One who alone can fulfill it:
We all want to live happily; in the whole human race there is no one who does not assent to this proposition, even before it is fully articulated.
How is it, then, that I seek you, Lord? Since in seeking you, my God, I seek a happy life, let me seek you so that my soul may live, for my body draws life from my soul and my soul draws life from you.
God alone satisfies.
From the Compendium:
361. What is the relationship between the beatitudes and our desire for happiness?
The beatitudes respond to the innate desire for happiness that God has placed in the human heart in order to draw us to himself. God alone can satisfy this desire.
Find the complete Catechism of the Catholic Church and the Compendium on the Vatican website at http://www.vatican.va/archive/ccc/index.htm