Radak: It is when enemies are around them to harm them, the angel comes, and they cannot harm them. This is like Daniel said "(6:23) "Elaki Shalach Mal'ache v'Sagar Pum Aryavasa", and it says "ha'Mal'ach ha'Go'el Osi mi'Kol Ra" (Bereishis 48:16).

Malbim: The angel is always around them like an armed camp to save them; they need not scream due to affliction. This hints to the people who joined with David after he fled Achish to Ma'aras Adulam (Shmuel I, 22:1-2).