John Calvin Commentary Acts 13:21

"And afterward they asked for a king: and God gave unto them Saul the son of Kish, a man of the tribe of Benjamin, for the space of forty years." — Acts 13:21 (ASV)

Afterward they desire. And this change was equivalent to them completely and clearly overthrowing the government which He had appointed, about which God Himself complains in Samuel (1 Samuel 8:5, 7).

But the stability of the election saved them from being punished as such madness deserved. Indeed, the wicked and unlawful desire of the people became for God a new and incredible occasion to establish the kingdom from which Christ would afterward come. For how did the scepter come to the tribe of Judah, except because the people desired to have a king? And certainly, the people acted wickedly; but God, who knows how to use evil things well, turned that offense into safety.

While Saul was overthrown from the kingdom, it served to rebuke the fault of the people (1 Samuel 15:28); but immediately when the kingdom was established in David’s family, the prophecy of Jacob was fulfilled (Genesis 49:10).