Acts 7:2-3 NAS95 And he said, “Hear me, brethren and fathers! The God of glory appeared to our father Abraham when he was in Mesopotamia, before he lived in Haran, (3) and said to him, ‘LEAVE YOUR COUNTRY AND YOUR RELATIVES, AND COME INTO THE LAND THAT I WILL SHOW YOU.’
In Stephen defense before the Sanhedrin, he said Abram lived in the city of Ur when God spoke to him the first time. Genesis gives us the whole account of what God said to him.
Genesis 12:1-3 NAS95 Now the LORD said to Abram, “Go forth from your country, And from your relatives And from your father’s house, To the land which I will show you; (2) And I will make you a great nation, And I will bless you, And make your name great; And so you shall be a blessing; (3) And I will bless those who bless you, And the one who curses you I will curse. And in you all the families of the earth will be blessed.”
God’s offer is simple and vague. Separate from your extended family to start a new life in new land and God will make him a great nation that will bless everyone on earth, but God did not offer details explaining how those blessings would come upon “all families of the earth.”
By the time God made this offer many cities had been established by those scattered at the Tower of Babel. The people who followed Nimrod knew how to make brick and build buildings. Abram was an astronomer and mathematician, who probably lived in a brick house. His neighbors were doctors, scribes, priests, secretaries, bookkeepers, accountants, lawyers, teachers. A British archeological team found 25,000 tablets and fragments inscribed in two different languages from the city of Ur. The tablets had literary and religious works. They were familiar with algebra and geometry. Medicine was taught in considerable detail. Other tables explained law, astronomy, and mathematics. The people of Ur were just like us except for the modern conveniences of automobiles, cell phones, etc.
If we know what happened at Babel, we can be sure Abram knew about the city that makes anything its citizens can imagine possible that Nimrod attempted to build. God offered Abram what Nimrod failed to attain. The opportunity to be part of a city built on foundations of justice God himself laid. Abram would have a name, and the citizens would have power to do anything they can imagine in a city inhabited by people who produce blessings instead of violence on the earth.
Hebrews 11:10 AMP For he [Abram] was [waiting expectantly and confidently] looking forward to the city which has foundations, [an eternal, heavenly city] whose architect and builder is God.
The offer was appealing and costly. Abram had to separate from his family and abandon the benefits of living in an established city. The advantages of living in a sophisticated society may have paled by a corrupt government that left its citizens in constant peril. The quarreling of the priests who served idols created instability. When they were not quarreling in the name of their pagan gods, the city struggled to hold foreign conquerors at bay. He had been living under foreign occupation for two decades when God spoke to him. The civil unrest created by the foreign occupation, and Abram’s conflict with the citizens of Ur over monotheism made moving to another land appealing, but not appealing enough to separate from his family.
Genesis 11:31AMP Terah took Abram his son, and Lot the son of Haran, his grandson, and Sarai his daughter-in-law, his son Abram’s wife; and they went out together to go from Ur of the Chaldeans into the land of Canaan; but when they came to Haran [about five hundred and fifty miles northwest of Ur], they settled there.
Abram left Ur but not his father’s house. Terah started the journey toward Canaan, but they never made it.
 Abraham: Father of Nations—and a Scientist, Mathematician and Astronomer | ArmstrongInstitute.org