Do not be afraid because of them! But who is “them”?

Do not be afraid because of them! That might sound good. But who said it? Who was it said to? Does it apply to us? And who is “them”? Who is it that we shouldn’t be afraid of? Oh yeah – why shouldn’t we be afraid? These are all good questions. Will we ask them? Or will we just run with the statement not to be afraid? Especially if we’re Christian and we know this comes from the Bible!