The title of this series is a little misleading. Actually, Angels are not allowed to have an opinion of their own - they are messengers - they deliver messages from God. In the New Testament we find them doing this in two different ways. Sometimes they come in dreams and sometimes they just show up and appear just the way they do in heaven. Whatever else we can say about angels they must recognize that they are a vital part of the miraculous Christmas story.
1 Peter 1:10-12
10 Of this salvation the prophets have inquired and searched carefully, who prophesied of the grace that would come to you, 11 searching what, or what manner of time, the Spirit of Christ who was in them was indicating when He testified beforehand the sufferings of Christ and the glories that would follow. 12 To them it was revealed that, not to themselves, but to us they were ministering the things which now have been reported to you through those who have preached the gospel to you by the Holy Spirit sent from heaven things which angels desire to look into.