Why do the heathen rage? The psalmist writes with a vision before his eyes. He "sees Jehovah upon his throne, and Messiah entering upon his universal dominion. The enemies of both on earth rise up against them with frantic tumult, and vainly strive to east off the fetters of their rule."
Hence his sudden outburst. "What ails the heathen (goim)," he says. "that they rage?" or "make an uproar" (Kay), or "assemble tumultuously" (margin of Authorized Version and Revised,Version)? What are they about?
What do they design? And why do the people—rather, the peoples, or "the masses" (Kay)—imagine (or, meditate) a vain thing? It must be "a vain thing;" i.e. a purpose which will come to naught, if it is something opposed to the will of Jehovah and Messiah.
The vision shows the psalmist Jew and Gentile banded together against the gospel of Christ. Its scope is not exhausted by the exposition of Acts 4:26, but extends to the whole struggle between Christianity on the one hand, and Judaism and paganism on the other.
"The peoples" still to this day "imagine a vain thing"—imagine that Christianity will succumb to the assaults made upon it—will fade, die away, and disappear.