Why was Abraham choosen?

We were talking after Turkey about Abraham being choosen to start the choosen people line and why Noah wasn't choosen. Generational DNA. Noah's generations were perfect.

Noah was given a commandment to replenish the earth, he and his three sons. Noah lived 350 years after the flood came.

Abraham was born only two short years after Noahs death.

Noah died in 1998 BCE
Abraham was born 1996 BCE

Noah lived to see Enos, Cainan, Mahalaleel, Jared, Lamech, Methuselah, Japheth, Shem,
Ham, Arphaxad, Gomer, Magog, Madai, Javan, Tubal Meshech, Tiras, Cush,
Mizraim, Canaan, Sidon, Nimrod, Heth, Phut, Salah, Eber, Peleg ( so he
would have not only experienced the flood, but also the separation of
the languages, and the earths continents), Reu, Serug, Nahor, Terah,
Haran, and Nahor, the brother of Abraham.

It is interesting that Abraham wasn't the firstborn, nor the second, but third born of Terah.

Jacob's third son was Levi. And the priesthood comes from this line. Certainly not because Levi was a righteous man, could it be because of being third born?

Only Leah had three sons, The concubines each had two as well as Rachel.

Moses was the third child of his mother, but not third son. Miriam born first then Aaron, then Moshe.