Genesis 13, Separation of Abram and Lot

God has sent Abram into Canaan, with a side trip to Egypt.

Genesis 13:1-4, Abram goes to the Negev and then to Bethel

So Abram went up from Egypt to the Negev, with his wife and everything he had, and Lot went with him. Abram had become very wealthy in livestock and in silver and gold. From the Negev he went from place to place until he came to Bethel, to the place between Bethel and Ai where his tent had been earlier and where he had first built an altar. There Abram called on the name of the LORD.

Abram travels from Egypt into the Negev (now southern Israel -- see this Wikipedia article.) The passage repeats previous descriptions of Abram's wealth.

Genesis 13: 5-13, Separation from Lot

 Now Lot, who was moving about with Abram, also had flocks and herds and tents. But the land could not support them while they stayed together, for their possessions were so great that they were not able to stay together. And quarreling arose between Abram's herdsmen and the herdsmen of Lot. The Canaanites and Perizzites were also living in the land at that time.

So Abram said to Lot, "Let's not have any quarreling between you and me, or between your herdsmen and mine, for we are brothers. Is not the whole land before you? Let's part company. If you go to the left, I'll go to the right; if you go to the right, I'll go to the left."

Lot looked up and saw that the whole plain of the Jordan was well watered, like the garden of the LORD, like the land of Egypt, toward Zoar. (This was before the LORD destroyed Sodom and Gomorrah.) So Lot chose for himself the whole plain of the Jordan and set out toward the east. The two men parted company: Abram lived in the land of Canaan, while Lot lived among the cities of the plain and pitched his tents near Sodom.

Now the men of Sodom were wicked and were sinning greatly against the LORD. 

The wealth of Abram and Lot, and the richness of the land, lead to quarrels. Abram suggests a solution and lets Lot choose. The passage records that Lot chose the whole plain of the Jordan and hints at problems to come, as Lot "pitched his tents near Sodom."

Alter notes that between Bethel and Ai is a viewpoint where one could easily to look out over the land. Lot sees the land to the east as "like the garden of the LORD"  (that is, Eden) even though it has wicked men living in it.

Genesis 13: 14-18, God's promise of eternal land, eternal offspring

The LORD said to Abram after Lot had parted from him, "Lift up your eyes from where you are and look north and south, east and west. All the land that you see I will give to you and your offspring forever. I will make your offspring like the dust of the earth, so that if anyone could count the dust, then your offspring could be counted. Go, walk through the length and breadth of the land, for I am giving it to you." So Abram moved his tents and went to live near the great trees of Mamre at Hebron, where he built an altar to the LORD.

God will bless Abram regardless of his choices; any choice is apparently a good one with God on his side! 

Abram is told to claim the land by walking through it.  Alter says that walking around the boundary of property was part of a legal ritual in the Ancient Near East.