"And Yahweh said to Abram, "Go out from your land and from your relatives, and from the house of your father, to the land that I will show you. ..... -.... And Abram went out as Yahweh had told him, and Lot went with him. Now Abram was seventy-five years old when he went out from Haran."
What qualifications did Abram have to be so chosen?

He was a descendant of Shem is all we are told at this point. It seems he was not even obedient to the initial call , because we see in Acts 7:2 the Spirit says through Stephen ".....The God of glory appeared to our father Abraham when he was in Mesopotamia, before he lived in Haran". It was after his father Terahs death that he moved out of Haran to Canaan at the age of 75.

I think the biggest qualification he had was his faith. At 75, we are usually thinking of moving to Florida and playing shuffleboard, let alone starting a second career! Belated though it was, he did move! He had Ishmael at the age of 86, and Isaac at 100. Till that time and even after, he wandered all over the land and we are not told he owned any of it except a plot of land he bought to bury Sarah and himself. Gen 21:34 says it like this "And Abraham dwelled as an alien in the land of the Philistines many days". He died at the age of 175.

Yet for a hundred years he trusted that God would fulfil his promise!

It wasn't perfect.... He was afraid, after He had waged war, and the Lord reassured him - "Do not be afraid, Abram; I am your shield, and your reward shall be very great." - Gen 15:1 He had his doubts about the promise of the heir, even openly asking the Lord,"O Yahweh, my Lord, what will you give me? I continue to be childless, and my heir is Eliezer of Damascus."- Gen 15:2 He had questions about his possessing the land - "And he said, "O Yahweh God, how shall I know that I will possess it?" Gen 15:8. And the Lord strengthened his faith by making a covenant with him.

But he always believed in the Lord, and He reckoned it to him as righteousness!

Faith will always be assailed by doubt. To doubt is natural because we have difficulty trusting that which we cannot see.Abrahams descendants did not possess the land till Moses wrote the book of Genesis, and even that possession is not the one God has been referring to. Abraham is still waiting!
But God's word is true and his promises sure. Abraham had and saw a son. We have seen the prophecy of the blessing to all families of the earth come through the Messiah, and by the justification that comes from faith. We wait for the final fulfillment in the confidence that it will come!

We can trust God, even if we sometimes doubt Him, and He is kind and knowing enough not to hold it against us, but gives us the blessing He has promised in His good and right time!