After rescuing Lot, a priest named Melchizedek blesses Abram with a sacrifice of bread and wine, and Abram gives him a tenth of everything. Heb 7:9ff says that Levi, who receives tithes, tithes through Abraham, and that if Christ is a priest forever after the order of Melchizedek (as Ps 110 says), He would have to have an indestructible life.
Abram knows that his descendents will be numerous, but he does not know that they will be his children, but God makes a covenant that Abram’s children will have the land, with Abram, in the middle of animals cut into portions, essentially declaring that if the covenant be broken, the same death will fall upon the person who breaks the covenant.
After this, Sarai, who was barren, suggests that Abram should try to have a child with her maid, Hagar. Sarai than demands that Abram choose between her and Hagar, and Abram tells Sarai that she may do with her maid as she chooses. Sarai deals harshly with Hagar, and Hagar flees, but an angel convinces Hagar to come back and submit, telling her that God will multiply her children as well.