The word for angel in the Hebrew can mean angel, messenger, or king, only the context decides the meaning. But the Angel of the LORD is very different. He is clearly not an ordinary angel. He is extraordinary. Unlike regular angels, if you can call an angel regular, the Angel of the LORD claims to be God [Ex 3:1-22], and He accepts worship [Judg. 13:16], no other angels ever makes these claims. If worship is offered to them, they correct the person, and advice them to worship God. [Rev. 19:10; 22:9]. Where the Angel of the LORD lights the fire. [Judge 6:21]
The Angel of the LORD presented himself as no other. Because of his unique behavior, scholars have come up with a more descriptive name, The Pre Incarnate Christ.