There are several key elements in this verse that we must consider. First, it is a covenant between God and Abram, and as such it cannot be abrogated by human effort. God indicated the terms of this covenant: The land that is promised was not given to Abram, but rather to his descendants. Although some may argue that this includes all of Abram's descendants, we know that the pact was passed on only to Isaac, then to Jacob (Israel) and his children. Abram did have other children, and the Ishmaelites are also descendants of Abram, but the Bible affirms that the covenant is passed through the son of promise – Isaac.
The next key element of the promise is that the land given by God was going to be acquired at a future time. "To your descendants" has no time limit! Just because it has not yet been fulfilled does not mean that it will not be fulfilled in coming years. Quite the contrary, we see that Israel's history perfectly follows God's plan as indicated in Deuteronomy 30:2-4, including the dispersion due to disobedience and regathering into the land because of the unchanging nature of the covenant:
"...and when you and your children return to the Lord your God and obey him with all your heart and with all your soul according to everything I command you today, then the Lord your God will restore your fortunes and have compassion on you and gather you again from all the nations where he scattered you. "
Just a century ago, the modern State of Israel did not exist, and half of the world’s Jewish population was obliterated by the Nazi Holocaust just a generation ago. But today Israel stands strong among the nations. The prophet Isaiah asks in 66:8,
"Who has ever heard of such a thing? Who has ever seen such things? Can a country be born in a day or a nation be brought forth in a moment?"
The answer is YES! Not because of Israel's might, but because of God faithfulness to His covenant.
What are the precise borders of the land promised to Abram’s descendants? The Lord makes them perfectly clear. Like any modern-day land purchase, the deed indicates the boundaries of the land given: from the Nile river (which is mainly modern Egypt and Sudan) to the Euphrates (modern-day Iraq).
To ensure that there is no doubt about the land’s boundaries, Scripture also indicates the different groups of people that occupy it: "...the land of the Kenites, Kenizzites, Kadmonites, Hittites, Perizzites, Rephaites, Amorites, Canaanites, Girgashites and Jebusites.” We know that these peoples lived in what is today Egypt, Sudan, Lebanon, Jordan, Syria, Iraq, part of Asian Turkey, and of course all of Israel, including Gaza and the West Bank.
This fact adds another dimension to the promise: the Lord is giving to Abram's descendants land that is currently occupied by other nations! The question arises of how Israel will acquire this land – will she have to invade and conquer other countries? The text in Genesis 15 offers no indication that Israel will have to fight and conquer; therefore, the logical answer is that the Lord will see that the promise is fulfilled.
The boundaries of the land promised to Abram's descendants is clearly indicated in the Bible, yet we know that Israel has never had control of the full extent of this land. The Lord never said when it will happen, but He does say that it will happen. I believe that after the final battles described in the Bible, when all the nations will rise against Israel, with the return of Jesus, Israel will prevail. The promise will be fulfilled with the establishment of His Messianic kingdom. If He has fulfilled every promise given thus far, we can be certain that He will fulfill those that remain – including all the land promised to Abram's descendants.