Doctrine of Life #60
60. That the stone tablets on which the law was written were called the Tablets of the Covenant, and that because of them the Ark was called the Ark of the Covenant, the law itself being the covenant, see Numbers 10:33; Deuteronomy 4:13, 23, 5:2-3, 9:9; Joshua 3:11; 1 Kings 8:19, 21; Revelation 11:19. And many other places.
The law was called a covenant because a covenant symbolizes conjunction. We are accordingly told regarding the Lord that He would be “as a covenant to the people” (Isaiah 42:6, 49:8). He is called, too, “the Messenger of the covenant” (Malachi 3:1), and His blood “the blood of the covenant” (Matthew 26:28, Zechariah 9:11, Exodus 24:4-10). That is why the Word is called the Old Covenant and New Covenant.
Covenants are also made as testaments of love, friendship, and fellowship, thus for the sake of conjunction.
Deuteronomy 5:19-23
20
"Neither shall you give false testimony against your neighbor.
21
"Neither shall you covet your neighbor's wife; neither shall you desire your neighbor's house, his field, or his male servant, or his female servant, his ox, or his donkey, or anything that is your neighbor's."
22
These words Yahweh spoke to all your assembly on the mountain out of the midst of the fire, of the cloud, and of the thick darkness, with a great voice: and he added no more. He wrote them on two tables of stone, and gave them to me.
23
It happened, when you heard the voice out of the midst of the darkness, while the mountain was burning with fire, that you came near to me, even all the heads of your tribes, and your elders;
