This demonstrates a problem Abraham appears to have had at the beginning of his conversion, showing that he was not perfect in his obedience. It also reveals God's patience in dealing with us, as well as how little control we sometimes exercise over some circumstances. In such times, we must continue trusting God and fighting to overcome as He leads us through them and teaches us aspects of His character.
Abraham's family members were outright pagans, as was Abraham before his conversion. We need to add Genesis 11:27-32 to the mix:
This is the genealogy of Terah: Terah begot Abram, Nahor, and Haran. Haran begot Lot. And Haran died before his father Terah in his native land, Ur of the Chaldeans. Then Abram and Nahor took wives: the name of Abram's wife was Sarai, and the name of Nahor's wife, Milcah, the daughter of Haran the father of Milcah and the father of Iscah. But Sarai was barren; she had no child. And Terah took his son Abram, and his grandson Lot, the son of Haran, and his daughter-in-law Sarai, his son Abram's wife, and they went out with them from Ur of the Chaldeans to go to the land of Canaan; and they came to Haran and dwelt there. So the days of Terah were two hundred and five years, and Terah died in Haran.
Barnes Notes contains a fairly complex study of these verses, showing that Abraham actually received his initial calling when he was 70 while living in Ur of the Chaldeans. Why "initial"? Verse 31 says they left Ur and then came to Haran, adding that Abraham's family dwelt there. "Dwelt" indicates that they remained there for an extended period—it was no mere overnight stop by a group of pilgrims at a motel.
Stephen's speech in Acts 7:2-4 helps us to understand:
Brethren and fathers, listen: The God of glory appeared to our father Abraham when he was in Mesopotamia, before he dwelt in Haran, and said to him, "Get out of your country and from your relatives, and come to a land that I will show you." Then he came out of the land of the Chaldeans and dwelt in Haran. And from there, when his father was dead, He moved him to this land in which you now dwell.
Stephen clearly states that God called Abraham before he dwelt in Haran, but Genesis 12:1 shows God then moved him from Haran after his father died. Apparently, Abraham's account to his father and others in the family—but most especially his father—of the things he was learning and believing in his calling persuaded them, despite being pagan to the core, that they, too, should emigrate to wherever God was leading Abraham.
Recall, however, from Isaiah 51:2 that God says that He called Abraham alone. Genesis 11:31 clearly shows Terah, the pagan patriarch of the family, leading the expedition, not Abraham. Abraham no doubt deferred to his father in this decision, but this was not God's will.
God knew that, because of Abraham's attitude, he would continue to defer to Terah. God did not want Terah's direct influence in what He was establishing through Abraham. Under Terah's pagan, patriarchal leadership, they got only as far as Haran from Ur, by itself an arduous 700-mile journey on foot!
Researchers speculate that the trip from Ur to Haran plus the sojourn there may have taken as long as five years before the party resumed the journey to Canaan. Perhaps Terah had a lengthy, lingering illness before dying. However, when the last leg of the journey was made, it was under Abraham's leadership.
God intends us to understand that the distance to the Promised Land—1,200 miles on foot from Ur to Canaan—plus the time spent getting there, illustrate the difficulty of breaking away from what we were to what God wants us to be. Unfortunately, some people never seem to accomplish the break.