The Mercy

Mercy is defined as kindness, affability, benedicence. The beatitudes of Matthew tell us a beatitude concerning mercy: Blessed are the merciful, for they shall be shown mercy. Matthew 5: 7.
The Mercy returns mercy, or expressed in another way: the spiritual gifts return spiritual gifts. The Spiritual gifts are perfections, explains Tomas Aquinas teacher of the scholastic. The beatitudes implicitly tell us about the  law of the return: you  reap what you saw. The right actions bring us blessings.
The Beatitudes carry a concept: happiness, but not happiness as a false good, but as a return, as a collateral effect. When we take the right, the correct actions we diminish, we minimize suffering, and as the opposite of happiness is suffering, when we decrease this last concept we predispose ourselves to happiness.
The minimization of the suffering is an ethical goal to achive happiness.
http://www.quintoevangelio.com.ar/en/articles/item/109-mercy.html