There are two lessons that jump out.
Then he proceeded from there to the mountain on the east of Bethel, and pitched his tent with Bethel on the west and Ai on the east; and there he built an altar to the Lord and called upon the name of the Lord.
Genesis 12:8 (NASB)
And he went on his journeys from the Negev as far as Bethel, to the place where his tent had been at the beginning, between Bethel and Ai, to the place of the altar which he had made there previously; and there Abram called on the name of the Lord.
Genesis 13:3-4 (NASB)
First, repeating things is a way to highlight the story. It’s underlined, bolded, italicized and blinking: REMEMBER THIS! A great famine will drive the people of God into Egypt, where a Pharaoh will take what is not his. But remember God’s mighty hand; you will be rescued. Remember!
Second, the rabbis say that “called upon the name of the Lord” can mean that Abram preached. He told people who God was.
But imagine how different his preaching was before and after being in Egypt. What lessons has Abram learned? Experience, suffering, seeing God rescue… these things change a person. They grow a person.
After the first altar, Abram is still willing to let his barren wife be taken away, fearing for his own life.
After the second altar, he is willing to accept a barren land, allowing Lot to take the fertile plain of the Jordan, trusting that God can turn barrenness into fruitfulness.