John Calvin Commentary Psalms 99:4

"The king`s strength also loveth justice; Thou dost establish equity; Thou executest justice and righteousness in Jacob." — Psalms 99:4 (ASV)

The king’s strength also loves judgment. This may be viewed as a threat designed to fill his enemies with dismay, as if he were to say, such is God’s regard for righteousness and equity, that he has clothed himself with power to avenge the injuries which his enemies have done to him.

I think it preferable, however, to apply it to the Church, because she is under the government of God for the express purpose of practicing righteousness and holiness. There is another interpretation which is by no means objectionable: namely, that which does not associate ideas of tyranny with the government of God, because there is constant concord between his power and justice.

But when I consider the whole context, I have no doubt that the prophet, after having introduced God as established upon his royal throne, now speaks of the manner in which he governs his kingdom. For he adds, thou hast established equity and righteousness. This clause is susceptible of two interpretations: either that God in his law has commanded his people to practice perfect equity, or that, in supporting and defending them, he has uniformly testified his great regard for his justice and equity.

It is certainly true that the highest equity has always characterized the works and judgments of God. Yet, it appears more probable that this refers to that system, that form of government, which God, who loves justice, appointed among the people of Israel. This system was the best rule for leading a life of honesty and integrity.

Therefore, the word to do is improperly taken to signify to order or command. If anyone chooses to consider this last clause as relating to God’s government, I am by no means inclined to disagree with him. For there is nothing that more animates and encourages the faithful to render obedience to God, or inspires them with greater zeal to observe his law, than to find in this course of action that they are the objects of his paternal care, and that the righteousness which he requires from his own people in words is, on his part, reciprocated by kind deeds.