God makes several promises to Abram (or Abraham as he is later known).

First of all, God promises that he will bless Abram and that anyone from any nation can be blessed through Abram:

Genesis 12 verses 1 - 3
1 Now the LORD said to Abram, “Leave your country, and your relatives, and your father’s house, and go to the land that I will show you. 2 I will make of you a great nation. I will bless you and make your name great. You will be a blessing. 3 I will bless those who bless you, and I will curse him who treats you with contempt. All the families of the earth will be blessed through you.”

God then shows Abram the land that he will give him and his offspring

Genesis 13 verses 14 - 17
14 The LORD said to Abram, after Lot was separated from him, “Now, lift up your eyes, and look from the place where you are, northward and southward and eastward and westward, 15 for I will give all the land which you see to you and to your offspring forever. 16 I will make your offspring as the dust of the earth, so that if a man can count the dust of the earth, then your offspring may also be counted. 17 Arise, walk through the land in its length and in its width; for I will give it to you.”

God then shows Abram how numerous his offspring will be:

Genesis 15 verse 5
5 The LORD brought him outside, and said, “Look now towards the sky, and count the stars, if you are able to count them.” He said to Abram, “So your offspring will be.”

God makes a covenant with Abram to give him and his offspring a specific area of land:

Genesis 15 verses 18 - 20
18 In that day the LORD made a covenant with Abram, saying, “I have given this land to your offspring, from the river of Egypt to the great river, the river Euphrates: 19 the land of the Kenites, the Kenizzites, the Kadmonites, 20 the Hittites, the Perizzites, the Rephaim,

God later repeats the promises he has made to Abram and emphasises these promises will never be broken:

Genesis 17 verses 3 - 8
3 Abram fell on his face. God talked with him, saying, 4 “As for me, behold, my covenant is with you. You will be the father of a multitude of nations. 5 Your name will no more be called Abram, but your name will be Abraham; for I have made you the father of a multitude of nations. 6 I will make you exceedingly fruitful, and I will make nations of you. Kings will come out of you. 7 I will establish my covenant between me and you and your offspring after you throughout their generations for an everlasting covenant, to be a God to you and to your offspring after you. 8 I will give to you, and to your offspring after you, the land where you are travelling, all the land of Canaan, for an everlasting possession. I will be their God.”

Abraham shows he trusts God enough to be prepared to sacrifice his son Isaac. Then God again repeats the promises and reminds Abraham that all nations can be blessed through his offspring:

Genesis 22 verses 15 - 18
15 The LORD’s angel called to Abraham a second time out of the sky, 16 and said, “ ‘I have sworn by myself,’ says the LORD, ‘because you have done this thing, and have not withheld your son, your only son, 17 that I will bless you greatly, and I will multiply your offspring greatly like the stars of the heavens, and like the sand which is on the seashore. Your offspring will possess the gate of his enemies. 18 All the nations of the earth will be blessed by your offspring, because you have obeyed my voice.’ ”