The whole episode in Genesis 15 is highlighted by the time stamp in verse 18, “On the same day the LORD made a covenant with Abram…” Yahweh declares that He has already given the land to Abram’s descendants. Therefore, as we have said, the covenant serves to reinforce and amplify the plain and clear word of God.
But what about the dimensions of the Promised Land? Can they be determined? If they can, can we say that Abram’s descendants have received it all? Has the gift ever been fully given?
The answer to the question in part hinges on what is meant in verse 18 by “from the river of Egypt to the great river, the river Euphrates.” Is the river of Egypt the Nile? Or is it a seasonal Wadi? The less usual term nahar for river (of Egypt) persuades most commentators that the Nile is not intended. Also, we should observe the fact that the adjective “great” (gadol) is used of Euphrates only and not the river of Egypt. It seems, then, as if this “river” is the Wadi mentioned in Num. 34:5; Josh. 15:4, 47, and 1 Ki. 8:65, and is what is known as the Wadi el-Arabah, which leads to the Gulf of Aqaba, circumscribing the area known as the Negev (south). So if we take the southern part of the land to be the Wadi el-Arabah, and the northern part to be the Euphrates, we must then ask whether this land area has ever been truly inherited by Israel at any time in its history, and if it is to be inherited in the future.
Unsurprisingly perhaps, supercessionists believe that the promise of inheritance has already been fulfilled:
Eventually, under Solomon, Israel claimed the land from the Euphrates to the border of Egypt, just as the Lord had promised originally to Abraham (Gen. 15:18; Ex. 23:31; cf. 1 Kings 4:21; 2 Chron. 9:26).
If it is indeed the case that Genesis 15:18-21 was fulfilled in Israel’s past then is there anything more to be said? Hasn’t that oath of God been satisfied? There are problems with such a view. One such difficulty is how anticlimactic the whole thing is. Abraham gets called away from his homeland with the promise of a land in which he will remain a sojourner all his life. The nation that springs from him spends four hundred years out of the land in Egypt. When they return they quickly apostasize and begin to splinter into factions. When they do finally “inherit” the whole piece of real estate in the days of David and only fully with Solomon (a mere eighty years maximum), it all ends with an unceremonious division of the nation and the land amid gradual declension until the descendants of Abraham are shipped off as captives back to pagan Mesopotamia in shame! In the history of nations this would be hardly worth a mention, let alone an honorable one. If the hope of the land covenant was extinguished so early, as Robertson and many other covenant theologians think, the fulfilling of God’s unilateral promise to Abram leaves little grounds for any tangible hope for Israel. It is one of the main purposes of the present book to show that this way of telling Israel’s story is fatally wrong.
Returning to the question of the land’s dimensions, Ronald B. Allen says that the land promise includes parts of ancient Aram as well as Canaan. He writes,
Although the period of conquest and the later expansions under Saul, David and Solomon began a fulfillment of the extent of the promises, the pattern was still only a partial fulfillment.
Citing Charles L. Feinberg, Allen believes the land promised in Genesis 15 would range over 300,000 square miles. This is considerably bigger than the land occupied at present by the nation of Israel. If Feinberg’s estimate was right, God would still have covenantal obligations in regard to the land coverage itself, never mind the promises of perpetuity included in the covenant.
As we have seen, it is an act of purely arbitrary interpretation to divide the seed promise from the land promise in this crucial chapter of Scripture. As far as the biblical history has come to this point, there is no reason to create such a cleavage in our understanding of the narrative. We must suspend judgment on what we think we know and allow the story to unfold at its own pace, marking carefully the outworking of God’s covenants as they come into view and drive the teleological and eschatological picture as it is steadily forming.
Genesis 16 contains the story of the birth of Ishmael. Ishmael was born after Abram had been in the land for ten years (16:3). He was not the son of Sarai but of her handmaiden Hagar. Like Adam many centuries before Abram had listened to his wife in contradiction to the word of God. The pragmatic solution which Sarai devised is still being felt by us today. This ought to remind us how placing our reasoning above the clear statements of God is always dangerous. It has been the cause of many theological errors. Despite the temptations to problem solve for God, we are never in a position to alter His timetable, nor His meaning. Basic hermeneutics should seek to be guided by this rule.
 Also known as Wadi el- Arish
 See David M. Fleming, “Wadi”, in Mercer Dictionary of the Bible, 951
 O. Palmer Robertson, Understanding the Land of the Bible, 9. It is not uncommon to find supercessionist author’s skipping the vital details of Genesis 15:8-21 in their argumentation. See also Peter J. Gentry & Stephen J. Wellum, Kingdom through Covenant, 423-424. An example of this is Sam Storms’ book, Kingdom Come.
 Ronald B. Allen, “The Land of Israel”, in Israel: The Land and the People, H. Wayne House, General editor, 24
 To cite John H. Sailhamer, “We must keep our eye on the author and follow him throughout his work.” – The Meaning of the Pentateuch, 154