Say among the heathen - Among the nations; all nations. Make this proclamation everywhere. This is changed from the parallel passage in 1 Chronicles 16. The language there is, “Fear before him, all the earth; the world also shall be stable, that it be not moved: let the heavens be glad, and let the earth rejoice: and let people say among the nations, The Lord reigneth.” The sense is, however, essentially the same. The idea here is, “Make universal proclamation that Yahweh is King.”
That the Lord reigneth - See the notes at Psalms 93:1.
The world also shall be established ... - Under the reign of God. The meaning is, that the world is fixed or immovable. It has its place, and it cannot be moved out of it. The government of God is fixed and stable. It is not temporary, changing, vacillating, like the dynasties of the earth, but is stedfast and abiding, and is well represented by the earth - so fixed and firm that nothing can move it from its place.
He shall judge the people righteously - The people of all lands; the nations of the earth. See the notes at Psalms 67:4.