Saint Pius X: “You shall love the Lord"

... your God, with all your heart,
with all your soul, and with all your mind.
This is the greatest and the first commandment.
The second is like it:
You shall love your neighbor as yourself.
The whole law and the prophets depend on these two commandments.”

-- Mt 22:34-40

When someone asks him, "Which commandment in the Law is the greatest?" Jesus replies: "You shall love the Lord your God with all your heart, and with all your soul, and with all your mind. This is the greatest and first commandment. And a second is like it: You shall love your neighbor as yourself. On these two commandments hang all the Law and the prophets." The Decalogue must be interpreted in light of this twofold yet single commandment of love, the fullness of the Law:

The commandments: "You shall not commit adultery, You shall not kill, You shall not steal, You shall not covet," and any other commandment, are summed up in this sentence: "You shall love your neighbor as yourself." Love does no wrong to a neighbor; therefore love is the fulfilling of the law.

-- CCC 2055