Why did an angel tell me to complete a mission in my dream?

Last night I had a dream about how some girl waved at me and smiled and smiled back at her then she walked towards me and started walking through the wall and appeared in a doorway in front of my house and I saw a bright light while she walked through it and I had a feeling she was an angel (she didnt have wings.) and I freaked out and said "omg what this isnt happening" and I just said a whole lot of stuff and I heard the girl say "i have a mission for u" .... And I woke up by my frightness and at the same time my alarm rang for school .. the dream felt so real. The girl had a colorful dress I think they kind of looked like the ones the use In the old days and she had long wavy orangish hair .. she was white and perfect teeth.