Charles H. Spurgeon on Psalms 99:1

Let the people tremble. Albeit the church be compassed about with enemies, as the lily among the thorns, yet because her Lord reigneth in the midst of her, she hath reason not only to comfort herself in him, but also hath ground of defying her enemies, and boasting against them: "The LORD reigneth; let the people tremble." The Lord's people do not worship an unknown God, they know who he is, and where to find him; to wit, in his ordinances, on the throne of grace, reconciling himself to the world in Christ: He sitteth between the cherubims. David Dickson.