God told Abraham way back in Genesis 15 that His descendants would be afflicted in a strange land for 400 years. We know from Exodus 12 that it was after 430 years of Egyptian bondage that God raised up Moses and used Him to deliver the Hebrews and lead them to the land of promise.
Along the way they came to a mountain in the wilderness of Sinai. There God gave Moses THE LAW that was to govern the nation of Israel in the land of promise. The Hebrews agreed to adhere to the commandments set forth by the Lord and that law became a covenant between God and the Israelite nation (Exodus 19:1-8; 24:3-8).
THIS WAS A CONDITIONAL COVENANT. Over and over God said that if the nation would keep this covenant and obey His laws that He would bless them with peace and prosperity and allow them to remain in the land of promise. He also promised to reward their rebellion with drought, oppression, and eventually removal from their homeland (Leviticus 26; Deuteronomy 29).
Now let's go back in our study. The Abrahamic covenant was an unconditional and everlasting promise that Abraham's multiplied seed would forever inherit the land of Canaan. But as they are getting ready to enter that land as a nation they make this conditional covenant with God, as described above. How do these two covenants relate to each other?
Galatians 3:16-19 answers, Now to Abraham and his seed were the promises made…And this I say, that the covenant, that was confirmed before of God in Christ, the law, which was four hundred and thirty years after, cannot disannul, that it should make the promise of none effect. For if the inheritance be of the law, it is no more of promise: but God gave it to Abraham by promise. Wherefore then serveth the law? It was added because of transgressions, till the seed should come to whom the promise was made; and it was ordained by angels in the hand of a mediator.
So the Mosaic covenant cannot disannul the Abraham covenant. Rather, we regard it is an amendment to the Abrahamic covenant, given to govern the nation of Israel in the promised land. Reading on in Galatians 3, we find that this law is given to serve man by both defining and restraining his sin and to bring him to Christ – the only One Who could deliver him from those sins and their eternal penalty.
Now I don't want to jump ahead too much, but I must point out that this covenant, though conditional, is everlasting. It will forever govern the nation of Israel in the land of promise. We read in Ezekiel and the other prophets of sacrifices and offerings being made in the temple during the millennial kingdom. We read in Isaiah 2 of Christ sitting upon the throne of His kingdom in Jerusalem, teaching men the law. We'll bring all this together (hopefully) when we look at the new and everlasting covenant.
This covenant was recorded on tables of stone (Exodus 34:27-28; Deuteronomy 4:13-18; Deuteronomy 9:9-11) and housed in the ark of the covenant (Deuteronomy 31:24-26; 1 Kings 8:9; 2 Chronicles 6:11). Israel's idolatry and immorality were referred to as transgressions of their covenant with God (Deuteronomy 17:2; Joshua 7:11, 15; Joshua 23:16; Judges 2:20; 1 Kings 19:10; 2 Kings 18:12; Psalm 78:10; Jeremiah 34:18; Ezekiel 16:59; Hosea 6:7; Hosea 8:1). And the sign of this covenant was the Sabbath (Exodus 31:12-18; Ezekiel 20:20).