For Thucydides the death and suffering of a great epidemic (just like war) test the moral health of individuals and of societies. And a people who are not morally strong, when they become afraid, quickly slip into lawlessness and sacrilege:
“For the violence of the calamity was such that men, not knowing where to turn, grew reckless of all law, human and divine. Men who had hitherto concealed what they took pleasure in, now grew bolder.”
The secret to happiness is freedom. The secret to freedom is courage.
Thucydides