How does Shamayim tell His virtue?
Radak: It rained hailstones, fire and sulfur on the Resha'im. Judging Resha'im until He eradicates them is His Tzedek and honor.
Malbim: It shows that the conduct of Shamayim and the Ma'arachah is not inevitable based on natural laws. Rather, it is arranged based on Tzedek and Mishpat. Reward and punishment are via Shamayim. Ba'alei ha'Tzava think that everything done in the lower world is the inevitable result of causes in the Ma'arachah. Shamayim does not consider Tzedek and straightness according to deeds. They cause what must result from their arrangement, even though it may lead to evil for a Tzadik and good for a Rasha. Shamayim will refute them.
Why does it say "v'Ra'u Kol ha'Amim Kevodo"?
Malbim: Ba'alei ha'Tzava think that every star influences and acts with its natural power over a small part of the earth, and only on one nation. Now all the nations will see His honor - He conducts the Ma'arachah according to His desire, based on His laws of Tzedek of the general conduct that encompasses all nations.
