The grace of the sacrament of Matrimony
"By reason of their state in life and of their order, [Christian spouses] have their own special gifts in the People of God." This grace proper to the sacrament of Matrimony is intended to perfect the couple's love and to strengthen their indissoluble unity. By this grace they "help one another to attain holiness in their married life and in welcoming and educating their children."
Source: Catechism of the Catholic Church (Vatican.va)