In Galatians 3, the Apostle Paul writes on this topic and reminds his readers that 430 years before God gave the Law, He made a promise to Abraham concerning his offspring. God did not make His promise contingent upon some future Law yet to be given, He made this promise of and by Himself. Galatians 3:16-19 Now the promises were made to Abraham and to his offspring. It does not say, "And to offsprings," referring to many, but referring to one, "And to your offspring," who is Christ. This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void. For if the inheritance comes by the law, it no longer comes by promise; but God gave it to Abraham by a promise. Why then the law? It was added because of transgressions, until the offspring should come to whom the promise had been made, and it was put in place through angels by an intermediary.
To fully understand this, we have to look at the covenant spoken of in the above passage, we find that in Genesis 15:18-21 On that day the LORD made a covenant with Abram, saying, "To your offspring I give this land, from the river of Egypt to the great river, the river Euphrates, the land of the Kenites, the Kenizzites, the Kadmonites, the Hittites, the Perizzites, the Rephaim, the Amorites, the Canaanites, the Girgashites and the Jebusites." This is the land blessing made to Abraham. The land promised extends from Egypt to the Euphrates River.