In the book of Genesis chapter 13 through 15 contains the substance of the Abrahamic Covenant.
The Covenant contains the promise to Abraham of a seed which shall be to great number and a land on which his seed will dwell. This is a promise almost too fantastic to believe because Abraham was advanced in years has no natural offspring through his beloved wife Sarah.
The Scripture tells us in Genesis 15:6 that Abraham believed the Lord and he counter to Him for righteousness. Abraham was Chaldean and have been a Chaldean for 75 years prior to time he entered the land of Canaan. God begun to work through him and in him to condition him to service but culturally Abraham was a Chaldean. When covenants were made in action Chaldean and throughout the, that past of civilize world. They were affirm and validated by the death of an animal or depending on the importance of the covenant numbers of animals.
Abraham's question to God, when God presents the agreement or covenant to him regarding the seed and the land especially it says 15:8,"O Sovereign Lord, how can I know that I shall gain possession of it?" And beginning of the verse 9 God said to Abraham, “Bring Me a heifer, a goat and a ram, each three years old along with a dove and a young pigeon. So God made Chaldean covenant with the Chaldean Abraham." So this covenant God made with Abraham because Chaldean Abraham will understand it. God begins to instruct Abraham to gather these animals together. Abraham understand the importance of the covenant because of the number of animals been gathered.
Those days when covenant were made, an animal was divided in half and the two parties making the covenant walked between the divided sections of the animal. In this way they were saying if you failed to bring about your responsibility in the covenant may this happen to you and the other party would say if you fail to bring about your responsibility in our agreement or covenant may this happen to you.
God instructed to Abraham in chapter 15 to divide these animals and we believe that Abraham fully expected to walk between these divided animals with God Himself. And had God and Abraham walked through the divided sacrifice together, it would have been a bilateral agreement or covenant and the fulfilling of the covenant would have been Priedieuculled on the fulfilling of the responsibility by both parties.
But when it came to walk through the covenant pieces, Abraham fell into a deep sleep and a thick and dreadful darkness came over him. Then the Lord said to him, "Know for certain that your descendants will be strangers in a country not their own, and they will be enslaved and ill-treated four hundred years. But I will punish the nation they serve as slaves, and afterwards they will come out with great possessions. You, however, will go to your fathers in peace and be buried at a good old age. In the fourth generation your descendants will come back here, for the sin of the Amorites has not yet reached its full measure.
A smoking brazier with a blazing torch appeared and passed between the divided pieces of animals and God Himself walked through the divided sacrifice.
On that day the Lord made a covenant with Abraham and said, "To your descendants I give this land, from the river of Egypt to the great river, the Euphrates, the land of the Kenites, Kenizzites, Kadmonites, Hitties, Perizzites, Rephaites, Amorites, Canaanites, Girgashites and Jebusites."
So the fulfilling of the promise made the Abraham to inhabit the land and to have a seed to numerable to count. It's not depending upon Abraham fulfilling his responsibility in the covenant he had none, but yet by this covenant God making it a covenant by passing alone through the divided pieces.
The promise of the land the seed was not set a side when the Jew didn't recognise Jesus Christ when He came to earth.
We cannot spiritually accept (appropriate) this promise made to the Jew to the church, this promise set aside for a while.
But later on when Jesus Christ rules and reigns on the earth, this promises made to Abraham will be latterly fulfilled.
Abraham got up from sleep with the knowledge that God had indeed confirmed the promise made to him for a seed and the land.
At the age of 76 Abraham believed that he need to help God to fulfil His covenant. But when we read the promises of God and rather than depend on him to bring them to past, believe that through the energy of the flash to need to give God a land and this was the downfall of Abraham.
Archaeologist have discovered that it was a custom of the day when wife was unable to give birth of child, for the wife to present the husband with maid servant through which the husband could have a male son so as to carry on the name of the family or house hold.
God promised to Abraham in Genesis chapter 15 that Abraham would have a seed and he would have a land but Abraham disobeyed to God or possible lack of faith allowed himself to become the father of Ishmael through Hagar the maid servant and it was not God's plan.
God doesn't need help from human instrumentality and because Abraham attempted to bring about God's covenant through the energy of the flash. We see in Genesis 16:16 that Abraham86 years of age when Hagar bore him Ishmael and we have 13 years of silence between the last verse of chapter 16 and first verse of chapter 17 where says when Abraham was 99 years of age, the Lord begun speak to him again, Abraham had 13 years in which to think over his disobedience and the wonder of the what final outcome would be and finally at the age of 99, God reconfirmed him the fact that He will bring about seed through Abraham and Sarah which will generate the nation of Israel.
Abraham thought God may bless him through Ishmael but God again reconfirmed will not be through Ishmael and assurance has given again that from Sarah a seed would be born named Isaac (Genesis 17:15) and name given advanced by God Himself on Genesis 17:21, the promise made to Sarah by God and the covenant that God has given to Abraham would be establish with Isaac.