Genèse 12:4

And Abram went, according as the Lord had spoken with him, and Lot went with him. And Abram was the son of seventy and five years at his going forth from Haran.

וילך אברם, he came as far as Charan where he left his father behind, and proceeded to the land of Canaan.

'כאשר דבר אליו ה, he did not ask G’d for further instructions thereby “testing” G’d, but continued on his journey because he believed that G’d would keep His promise as He had said.

בצאתו מחרן, perhaps, prior to leaving his father behind, he had spent a few days trying to convince him to come along with him. At the time he left Charan he was 75 years old. [it is hard to see why he would have tried to persuade his father to come along, as he then would not have complied with the commandment to leave his father’s house. Ed.]

ואברם בן חמש שנים ושבעים שנה בצאתו מחרן “and Avram was seventy five years old when he left Charan.” At first glance this statement is puzzling as the covenant of the pieces is reported as if it had occurred later than Avram’s departure from Charan (chapter 15). According to our tradition it took place 30 years before the birth of Yitzchok, and this is what the statement that the Israelites spent 430 years in Egypt, reported in Exodus 12,40 is based on. We know as a fact from the Torah that Avraham was one hundred years old when Yitzchok was born. According to Rashi, thirty years elapsed between the covenant of the pieces and the birth of Yitzchok. If so, Avraham could not have been more than 70 years old at that event. Lot joined him and was taken captive after having separated from Avraham during that same year still, and Avraham defeated the armies which had taken him captive, after which event G–d appeared to him as reported in chapter 15. He returned to Charan once more, and when he was 75 years old, G–d commanded him to move to the land of Canaan, i.e. “the land which I will show you.” (12,1) I have found confirmation of these dates in the book called Seder Olam, an ancient historical record, considered reliable by our sages. I am quoting verbatim from that text: “Avraham was 48 years old when G–d confused the languages of the people and they moved apart from one another. When G–d spoke to him at the covenant of the pieces, he was 70 years old. (this was while he was on the soil of the land of Canaan). He returned to Charan where he stayed for another five years. It follows that 27 years elapsed between the destruction of the Tower and Avraham’s departure from Charan a second time” Our verse refers to the second departure.