NOTES for Psa 99
The Lord is called the One who reigns, and this means that however many kingdoms there may be on earth, and however highly their rulers may exalt themselves, He alone is the One who truly reigns over the world. But He is above earthly kings not only in power and majesty. The most important quality of His Kingdom, one that is difficult to achieve in human societies, is justice, and this alone places it above earthly kingdoms. Yet His justice surpasses our customary ideas about what justice should be: supreme justice is inseparable from mercy. The psalmist calls the Lord both forgiving and punishing, and we should note that forgiveness is mentioned first.
Although the Lord revealed Himself to prophets called from among one particular people, He is not only their God: through the Jewish people the Lord revealed Himself to all humanity. Moses and Aaron, prophet and priest, are not mentioned side by side here by chance. The ministry of each is important and necessary; each, in his own place, served the One who called them and guarded the truth entrusted to them. They did not guard it as esotericists guard "secret knowledge," fearing that someone might penetrate mysteries hidden from the uninitiated. No, Moses and Aaron, and their successors, kept the truth pure so that it might become the possession of the whole people and, in time, of other nations as well, so that they too might in due course acknowledge who their true King is.