John Calvin Commentary Acts 7:4

"Then came he out of the land of the Chaldaeans, and dwelt in Haran: and from thence, when his father was dead, [God] removed him into this land, wherein ye now dwell:" — Acts 7:4 (ASV)

Then going out. The readiness and willingness of faith are commended in these words. For when he was called, he made no delay, but made haste and subdued all his inclinations, so that they might obey the holy commandment of God.

It is uncertain for what reason he stayed at Haran. It may be that his father's weakness caused him to remain there (who, as we read, died there shortly after). Alternatively, it could be because he dared not go further until the Lord had told him where he should go.

In my opinion, it is more likely true that he was delayed there for a while by his father's weariness and sickness, because Stephen plainly says that he was brought from there after his father's death.