24 We do not think it essential to Our subject to cite at length passages from the Old Testament books which contain truths divinely revealed in ancient times. We consider it sufficient to call to mind that the covenant made between God and the people and sanctified by peace offerings - the first Law of which was written on two tablets and made known by Moses(17) and explained by the prophets -was an agreement established not only on the strong foundation of God's supreme dominion and of man's duty of obedience but was also based and nourished on more noble considerations of love. The ultimate reason for obeying God, for the people of Israel, was not the fear of divine vengeance which the rumble of thunder and the lightning flashing from the top of Mount Sinai struck into their souls, but was rather the love they owed to God. "Hear, O Israel ! The Lord our God is one Lord. Thou shalt love the Lord, thy God, with thy whole heart, and thy whole soul, and thy whole strength. And these words which I command thee this day shall be in thy heart."(18)
Source: Haurietis Aquas (Vatican.va)