He will cut off [1] the spirit of princes. As the Hebrew word vtsr, batsar, occasionally signifies to strengthen, some think it should be so translated in this passage. But as in the two clauses of the verse the same sentiment is repeated, I have no doubt that by the first clause is meant that understanding and wisdom are taken away from princes; and that by the second, God is represented in general as terrible to them, because he will cast them down headlong from their loftiness. As the first thing necessary to conduct an enterprise to a prosperous issue is to possess sound foresight, in which the people of God are often deficient from the great perplexity in which they are involved in the midst of their distresses, while, on the other hand, the ungodly are too sharp-sighted in their crafty schemes; it is here declared that it is in the power of God to deprive of understanding, and to inflict blindness on those who seem to surpass others in acuteness and ingenuity. The majority of princes being enemies to the Church of God, it is expressly affirmed, that He is sufficiently terrible to subdue all the kings of the earth. When it is said, that their spirit is cut off, or taken away from them, it is to be limited to tyrants and robbers whom God infatuates, because he sees that they apply all their ingenuity and counsels to do mischief.

Footnotes

1 - The word employed by Calvin is "Vindemiabit," which expresses the precise idea of the original verb, yvtsvr, yebtstor It is from vtsr, he cut off, brake off, referring properly to grapes and other fruits. The reading of the LXX. is, "takes away."

He shall cut off the spirit of princes - That is, He will cut down their pride; he will break them down. Luther renders it, "He shall take away the wrath of princes." The allusion is to what he had done as celebrated in this psalm. He had shown that he could rebuke the pride and self-confidence of kings, and could bring them low at his feet.
He is terrible to the kings of the earth - When they are arrayed against him.
(1) they are wholly under his control.
(2) he can defeat their plans.
(3) he can check them when he pleases.
(4) he can, and will, make their plans - even their wrath - the means of promoting or carrying out his own purposes.
(5) he will allow them to proceed no further in their plans of evil than he can make subservient to the furtherance of his own.
(6) he can cut down the most mighty of them at his pleasure, and destroy them forever.

He shall cut off the spirit of princes - Even in the midst of their conquests, he can fill them with terror and dismay, or cut them off in their career of victory.
He is terrible to the icings of the earth - "He is the only Ruler of princes;" to him they must account. And a terrible account most of them will have to give to the great God; especially those who, instigated by the desire of dominion, have, in the lust of conquest which it generates, laid countries waste by fire and sword, making widows and orphans without number, and extending the empire of desolation and death.
Thus all are under his dominion, and are accountable to him. Even those whom man cannot bring to justice, God will; and to judge them is one grand use of a final judgment day.

He shall (i) cut off the spirit of princes: [he is] terrible to the kings of the earth.
(i) The Hebrew word signifies "to vintage or gather grapes" meaning that he will make the counsels and enterprises of the wicked tyrants foolish and vain.

He shall cut off the spirit of princes,.... The pride of their spirits, as the Targum, humble their proud spirits, and bring them down; or dispirit them, take away their courage from them, upon which they flee apace to rocks and mountains to cover them; or confound them, blast their schemes, and carry their counsel headlong, and even take away their breath, or life; which he can as easily do as a man can cut off a bunch of grapes from the vine, as the word (g) here used signifies; the destruction of the wicked is expressed by cutting down the vine of the earth, and casting it into the winepress of God's wrath, Revelation 14:17,
he is terrible to the kings of the earth; as he was to the king of Assyria, when he sent his angel, and destroyed his army; and as he has been to others in all ages; so he will be to the kings of the earth that have committed fornication with the whore of Rome, who will be in the utmost panic at the time of her destruction, Revelation 18:9, and who will themselves be overcome by the Lamb, Revelation 16:14. The Targum is, he is to be feared above all the kings of the earth.
(g) "qui vindemiat", Junius & Tremellius, Piscator; "succidet nempe, ut vindemiator racemos", Vatablus, so Ainsworth.

Cut off - As men do their grapes in time of vintage; so the Hebrew verb implies. The spirit - Their breath and life, as he did in the Assyrian army.