Albert Barnes Commentary Luke 21:18

"And not a hair of your head shall perish." — Luke 21:18 (ASV)

A hair of your head perish. This is a proverbial expression, denoting that they should not suffer any essential injury. This was strikingly fulfilled in the fact that, in the calamities of Jerusalem, there is reason to believe that no Christian suffered. Before those calamities came upon the city, they had fled to Pella, a city on the east of the Jordan. See Barnes on Matthew 24:18.