The quote is referring to traders from Athens around 490-470 B.C. whose travels gave them a sense of the variability (and similarity) of humans, their beliefs and cultures. This greater sense of the world around them made these traders immune from some of the orthodoxy of various sects that eventually led to events like the inquisition.
I think the quote appeals to me because at my advanced age I also have the feeling I've seen too much to believe too much.
After the events of 2015-2016 I devoted a lot of time to trying to understand what happened in our country that led us to that place. I kept stepping further back in history until I ended up devoting more time to figuring out what happened over the last 2000 years than the last 20 years (days, minutes...).
I still haven't got "the answer" or even the question nailed down but I got a feeling.
Skepticism, compassion, as much joy as you can find, and a sense of equanimity are probably appropriate responses to a complicated world.
Oh but it's still good to dream...