Today's popular view of angels is that they are supernatural beings with various powers.
But the Biblical word מַלְאָךְ, mal'ak, can simply mean "messenger" or "agent", and it is translated as such in many verses. In fact, in most places where the word is usually translated as "angel", it would make as much sense to use either of those other words.
These messengers could be considered as ad hoc prophets delivering a simple message.
Are there any instances where an angel was required to be something more than simply a human being chosen to represent, or chosen to deliver a message from, the Lord?