Radak: The author prays to bring the redemption close and take vengeance from the Resha'im. So the Nevi'im promised - "v'Hayu Chol Zedim v'Chol Oseh Rish'ah Kash v'Lihet Osam ha'Yom ha'Ba" (Mal'achi 3:19).

Malbim: It gives claims of those who deny Hashgachah. They 'prove' from the success of Resha'im and afflictions of Tzadikim that Hashem does not oversee the world. The Mizmor rebuts this. This is why it is next to Mizmor Shir l'Yom ha'Shabbos (92:1); all three of these (including Mizmor 93 - PF) are the same matter.

Radak: You have the ability to take vengeance.

Radak (91:1, citing Shocher Tov): Moshe said this corresponding to Shevet Gad, from which comes Eliyahu ¹ , who will take vengeance against the nations.

Rashi: Show and reveal to us Your vengeance.

Malbim: Sinners say, why is Hashem silent to Resha'im? It is proper that He appear and punish them, for three reasons. (a) He is "Kel Nekamos." Also refer to 94:2:2:1, 94:3:1:2.