John Calvin Commentary Isaiah 28:6

"and a spirit of justice to him that sitteth in judgment, and strength to them that turn back the battle at the gate." — Isaiah 28:6 (ASV)

And for a spirit of judgment. He explains how the Lord will adorn that “remnant” with additional splendor; for he presents examples of the true art of civil government, which mainly contributes to the support of nations. It consists mainly of two things, counsel and strength. The internal administration must be conducted by counsel and wisdom, and “strength” and force are needed against external enemies.

Therefore, since it is by these two defenses that kingdoms and commonwealths defend and maintain their standing, he promises to his people the spirit of “wisdom” and “strength.” At the same time, he shows that it is God who gives both, and that they should not be expected from any other source; for magistrates will not be able to rule and administer justice in a city, and military generals will not be able to repel enemies, unless the Lord directs them.