The word Angel
In the Hebrew language in which the Old Testament was written, the word translated as 'angel' is the word 'Mala’ak'. This word can also be translated as 'messenger'. In the Greek of the New Testament the word translated as 'angel' is the Greek 'angelos', which too can be translated as messenger.
The important point here is that while the word 'angel' in the Bible may mean a supernatural being, it may also refer to a human being.
An example of the application of the word to a human being appears in the prophecy of Malachi:
"For the lips of a priest should guard knowledge, and people should seek instruction from his mouth, for he is the messenger of the LORD of hosts." (Malachi 2:7)
The high priest was required to be a descendant of Aaron the brother of Moses, which means that he was a human being. He was given the task of communicating the word of God to the people of Israel, so he is described here as a messenger. The Hebrew word for 'messenger' is the word which is elsewhere translated 'angel'.