Why did trade often lead to cultural exchange?

Merchants carried information as well as products.they could gain knowledge of different religions practiced in the cities they visited.
judaism christianity spread this way 

Communicating with the dead was common, it wasn’t seen as bizarre or weird,” explains murch. “it’s hard to imagine that now, we look at that and think, ‘why are you opening the gates of hell? ’

An example of a political opponent would be albert einstein hitler hated him because he was jewish a pacifist