‘ Arise, O YHWH; Do not let man prevail:
Let the nations be judged in your sight.
Put them in fear, O YHWH:
Let the nations know themselves to be but men. Selah.
The Psalm finishes with a cry to YHWH to bring about these purposes, and deal with the unrighteous nations. Let YHWH arise and prevent man from prevailing, for he is unrighteous and will behave unrighteously. Let Him judge them in accordance with their deserving, as known by the all-seeing eye. Indeed let Him put them in fear and make them recognise that they are but men. Let see themselves in a proper perspective. For then there would be a hope that some would hear the declaration among them of His doings (Psalms 9:11) and recognise their need, and hear and respond to YHWH.
This is not a vindictive cry. It is a prayer for the deliverance of the righteous. He wants the nations to recognise that they are dealing with the anointed of YHWH and cannot therefore prevail. They may boast about their greatness but they are but men. And thus when their belligerence results in judgment they will be made to recognise the fact. The people of God will win in the end.
For the truth is that it is only when men are finally brought to a true judgment concerning themselves that the everlasting kingdom of righteousness can be established. It was a feature of the Davidic kingship that in the end not only Israel but the whole world that had not been judged and condemned was to be blessed through it once the unrighteous had been dealt with (Psalms 2:8-12).