The new covenant not so much improved as exploded out of the old covenant to give life to the world. The new covenant is more glorious than anything conceived before. That God would himself come into the world and die for the benefit of his people is the glory that surpasses that of Moses. Second Corinthians chapter three tells the story in brief.
The Decalogue in Sacred Scripture
2056 The word "Decalogue" means literally "ten words."11 God revealed these "ten words" to his people on the holy mountain. They were written "with the finger of God,"12 unlike the other commandments written by Moses.13 They are pre-eminently the words of God. They are handed on to us in the books of Exodus 14 and Deuteronomy.15
Beginning with the Old Testament, the sacred books refer to the "ten words,"16 but it is in the New Covenant in Jesus Christ that their full meaning will be revealed.
2057 The Decalogue must first be understood in the context of the Exodus, God's great liberating event at the center of the Old Covenant. Whether formulated as negative commandments, prohibitions, or as positive precepts such as: "Honor your father and mother," the "ten words" point out the conditions of a life freed from the slavery of sin. the Decalogue is a path of life: If you love the LORD your God, by walking in his ways, and by keeping his commandments and his statutes and his ordinances, then you shall live and multiply.17 This liberating power of the Decalogue appears, for example, in the commandment about the sabbath rest, directed also to foreigners and slaves: You shall remember that you were a servant in the land of Egypt, and the LORD your God brought you out thence with a mighty hand and an outstretched arm.18
2058 The "ten words" sum up and proclaim God's law: "These words the Lord spoke to all your assembly at the mountain out of the midst of the fire, the cloud, and the thick darkness, with a loud voice; and he added no more. and he wrote them upon two tables of stone, and gave them to me."19 For this reason these two tables are called "the Testimony." In fact, they contain the terms of the covenant concluded between God and his people. These "tables of the Testimony" were to be deposited in "the ark."20
2059 The "ten words" are pronounced by God in the midst of a theophany (“The LORD spoke with you face to face at the mountain, out of the midst of the fire."21). They belong to God's revelation of himself and his glory. the gift of the Commandments is the gift of God himself and his holy will. In making his will known, God reveals himself to his people.
2060 The gift of the commandments and of the Law is part of the covenant God sealed with his own. In Exodus, the revelation of the "ten words" is granted between the proposal of the covenant 22 and its conclusion - after the people had committed themselves to "do" all that the Lord had said, and to "obey" it.23 The Decalogue is never handed on without first recalling the covenant (“The LORD our God made a covenant with us in Horeb.").24
2061 The Commandments take on their full meaning within the covenant. According to Scripture, man's moral life has all its meaning in and through the covenant. the first of the "ten words" recalls that God loved his people first: Since there was a passing from the paradise of freedom to the slavery of this world, in punishment for sin, the first phrase of the Decalogue, the first word of God's commandments, bears on freedom "I am the LORD your God, who brought you out of the land of Egypt, out of the house of slavery."25
2062 The Commandments properly so-called come in the second place: they express the implications of belonging to God through the establishment of the covenant. Moral existence is a response to the Lord's loving initiative. It is the acknowledgement and homage given to God and a worship of thanksgiving. It is cooperation with the plan God pursues in history.
2063 The covenant and dialogue between God and man are also attested to by the fact that all the obligations are stated in the first person (“I am the Lord.") and addressed by God to another personal subject (“you"). In all God's commandments, the singular personal pronoun designates the recipient. God makes his will known to each person in particular, at the same time as he makes it known to the whole people: The Lord prescribed love towards God and taught justice towards neighbor, so that man would be neither unjust, nor unworthy of God.
Thus, through the Decalogue, God prepared man to become his friend and to live in harmony with his neighbor.... the words of the Decalogue remain likewise for us Christians. Far from being abolished, they have received amplification and development from the fact of the coming of the Lord in the flesh.26
http://www.vatican.va/archive/ENG0015/__P78.HTM
