In the dialogue’s final paragraphs, Critias talks about the people of Atlantis coming together to create a great society because they are virtuous and they have respect for their laws—but when they lose their virtue and their respect for the laws, Atlantis is doomed. This point of view connects this dialogue with Plato's Republic in which Socrates draws a similar conclusion about the importance of virtue and rule of law for the ideal city-state.
Here are the final two paragraphs from Critias:
For many generations and as long as enough of their divine nature survived, they were obedient unto their laws and they were well disposed to the divinity they were kin to. They possessed conceptions that were true and entirely lofty. And in their attitude to the disasters and chance events that constantly befall men and in their relations with one another they exhibited a combination of mildness and prudence, because, except for virtue, they held all else in disdain and thought of their present good fortune of no consequence. They bore their vast wealth of gold and other possessions without difficulty, treating them as if they were a burden. They did not become intoxicated with the luxury of the life their wealth made possible; they did not lose their self-control and slip into decline, but in their sober judgment they could see distinctly that even their very wealth increased with their amity and its companion, virtue. But they saw that both wealth and concord decline as possessions become pursued and honored. And virtue perishes with them as well.
Now, because these were their thoughts and because of the divine nature that survived in them, they prospered greatly as we have already related. But when the divine portion in them began to grow faint as it was often blended with great quantities of mortality and as their human nature gradually gained ascendancy, at that moment, in their inability to bear their great good fortune, they became disordered. To whoever had eyes to see they appeared hideous, since they were losing the finest of what were once their most treasured possessions. But to those who were blind to the true way of life oriented to happiness it was at this time that they gave the semblance of being supremely beauteous and blessed. Yet inwardly they were filled with an unjust lust for possessions and power. But as Zeus, god of the gods, reigning as king according to law, could clearly see this state of affairs, he observed this noble race lying in this abject state and resolved to punish them and to make them more careful and harmonious as a result of their chastisement. To this end he called all the gods to their most honored abode, which stands at the middle of the universe and looks down upon all that has a share in generation. And when he had gathered them together, he said…
(Plato: Complete Works; Edited by John M. Cooper and D. S. Hutchinson; “Critias,” Translated by Diskin Clay; Page 1306)We don’t know what Zeus said at the conclave of the gods. Significant part of this dialogue is missing because in the beginning of the dialogue Socrates says that the fourth person in the dialogue, a man called Hermocrates, will have a chance to speak after Critias. But we never hear from Hermocrates.