what's in a name?

 Or, what IS a name?

I was reading in Exodus, chapter twenty-three. Verses 20 + 21: I am going to send an angel in front of you, to guard you on the way and to bring you to the place that I have prepared. Be attentive to him and listen to his voice; do not rebel against him, for he will not pardon your transgression; for my name is in him.

I find this so interesting, and puzzling. What does that mean? 

Why does God say we should call upon the name of the Lord?  Why doesn't he just say we should call upon him?  If I see you at a distance, and call, I call you, not your name. I am calling to you, yourself. I may call out your name, or to put it differently, I may call you by your name, but I'm not calling on your name, so what does that mean?

Somebody recommended a book to me called God Has a Name, by John Mark Comer - it was somewhat helpful (although I don't remember how - guess I need to reread!), but I still have the question. And today in Exodus, there it was again, "my name is in him". I really feel that this is something we don't understand; that there is more to a name than we realize. 

But I'm not the one to figure it out.