John Gill Commentary Luke 1:12

"And Zacharias was troubled when he saw [him], and fear fell upon him." — Luke 1:12 (ASV)

And when Zacharias saw him
The angel; he was troubled, and fear fell upon him; for such appearances of angels were not now so common as formerly: and when they were more usual, generally had such effects on the minds, even of good men; see (Judges 6:22) (Daniel 8:17) .