No dictator, no invader can hold an imprisoned population by force of arms forever. There is no greater power in the universe than the need for freedom. Against that power, governments and tyrants and armies cannot stand. The Centauri learned this lesson once. We will teach it to them again. Though it take a thousand years, we will be free.
I love this scene for so many reasons the main being that it shows the surprising true nature of the characters.
1. Vorlons are powerful.
2. G'Kar and Na'toth are truly devastated at the loss of the potential for their people to live forever but also gaining the upper-hand on the other races.
3. The most surprising in my view, which is that of Londo the most ambitious character in the whole show is not at all phased at losing the potential for him and his people being able to live forever. In fact Londo seems over joyed about the whole thing maybe because everyone was going too crazy over it or perhaps because the Narns suffer once again.
4. Sinclair and Garibaldi are just so happy but restrained.
5. This is the clearest answer we get from Kosh in the whole show.
6. This scene shows us the Vorlons trying to protect us from our own choices.