99:1 The Lord reigns. See notes Ps. 5:2 and 93:1.

upon the cherubim. Cherubim are spiritual beings who dwell in heaven with God. They are guardians of God’s holiness, as witnessed by their role in protecting the post-Fall garden (Gen. 3:24). Cherubim were symbolically represented in the tabernacle, both in the innermost curtain (Ex. 36:35), and in the Most Holy Place (Ex. 37:1–9). The psalm refers to the cherubim of God’s throne with their outstretched wings above the ark of the covenant.

let the earth quake. At God’s special self-revelations (theophanies) reverberations, like those of a natural earthquake were sometimes felt throughout the earth. See “The Greatness of God” at 1 Chr. 29:11.