1)
They already saw the angel "Mafli La'asos" (do wonders). Why did they fall on their faces, and Mano'ach thought that they will die, only after the angel ascended in the flame?
1.
Malbim: See an angel when he leaves [his physical garment] is much greater than seeing him in his physical garment. Flesh and blood cannot see what is purely spiritual. Refer to 6:22:3:3 and the notes there.
