John Calvin Commentary Psalms 78:71

"From following the ewes that have their young he brought him, To be the shepherd of Jacob his people, and Israel his inheritance." — Psalms 78:71 (ASV)

He took him from following the suckling ewes, etc. The grace of God is further commended by the circumstance that David, who was a keeper of sheep, was made the shepherd of the chosen people and heritage of God. There is an allusion to David’s original condition; but the Spirit of God, at the same time, shows us the difference between good and lawful kings, and tyrants, robbers, and insatiable extortioners, by telling us that whoever would aspire to the character of the former must be like shepherds.

It is later added (Psalms 78:72) that David had faithfully performed the duties of the trust committed to him. By this the prophet indirectly rebukes the ingratitude and perverseness of the people, who not only overturned the holy and inviolable order which God had established, but who had also, in shaking off his salutary yoke, thrown themselves into a state of miserable dispersion.

What follows concerning the prudence of David’s hands seems to be an improper form of expression. But it is intended to express forcefully that he was not only successful in what he undertook, but was also governed by the Spirit of God. This Spirit prevented him from putting his hand at random to any work that might come his way and led him prudently and skilfully to do what faith and duty called him to. Thus, in the success of his undertakings, his wisdom appears more conspicuous than his good fortune.