Psalms 9:20

Put them in fear, O Lord
Who are, a bold, impudent, fearless generation of men; who, like the unjust judge, neither fear God nor regard men, therefore the psalmist prays that God would inject fear into them, who only can do it; and this will be done at Babylon's destruction, when the antichristian kings, merchants, and seafaring men, will stand afar off for fear of her torment, ( Revelation 18:10 Revelation 18:15 Revelation 18:17 ) ;

[that] the nations may know themselves [to be but] men;
and not God, and have no power against him; see ( Isaiah 31:3 ) ; the sense is, that the antichristian nations, who oppose themselves to Christ and his people, may know that they are but frail, mortal, miserable men, as the word ^F17 signifies; and that he who is at the head of them, the man of sin, is no other, though he exalts himself above all that is called God, ( 2 Thessalonians 2:4 ) ; or these words are a prayer for the conversion of many among the nations, and may be rendered, "put, O Lord, fear in them" ^F18; that is, the true grace of fear, "that the nations may know" themselves, their sin and guilt and danger, and know God in Christ, and Christ, and the way of salvation by him; for at the word "know" should be a stop, concluding a proposition, since the accent "athnach" is there; and then follows another, "they [are] men. Selah": destitute of the fear and grace of God, are capable of it, but cannot give it to themselves.

Selah; on this word, (See Gill on Psalms 3:2).