1 Cor 6:3 Do you not know that we will judge angels? How much more the things of this life!
This is such an interesting discussion, because the topic of angels is so often treated as set-in-stone. I don't remember any pastors teaching that an angel might have mixed motives, or free will.
But look at the collection of verses above -- these show that an angel has a choice. They deliver messages, but might also have the temptation to stick around longer and deliver their own messages -- who knows. They are dispatched.
We tend to be very trusting of things larger and more powerful than ourselves.
I think back to times in church history where people spoke of named angels returning to revival services over and over... and at some point, things went wrong. People leaned on the angels' assistance and were flattered by this direct contact; but it was God that was the source of miracles.
And look at the visitations of Joseph Smith and Muhammad -- they took the angels' words as truth, and got carried away in a direction that conflicted with prior established truths.
Hebrew Mal'ak = messenger, representative
Greek aàggelov = a messenger, envoy, one who is sent, an angel, a messenger from God
"When Jesus was being arrested by His enemies, Peter tried to defend Him by using a sword. Jesus responded by telling Peter His Father was perfectly able to send more than twelve legions of to His defense (Matt. 26:53). In the time of Caesar Augustus, one legion of men equaled 6826. Jesus could have been rescued by roughly 82,000 angels!"
We are warned not to worship angels, even though they are encamped around us.
Colossians 2:18 Do not let anyone who delights in false humility and the worship of angels disqualify you for the prize. Such a person goes into great detail about what he has seen, and his unspiritual mind puffs him up with idle notions.
Rev. 19:10
And I fell before his feet (angel) to worship him, but he said to me, Behold! Stop! I am a fellow-slave of yours, and of your brothers, having the testimony of Jesus. Worship God. For the testimony of Jesus is the spirit of prophecy.
Thorough articles here:
CATHOLIC ENCYCLOPEDIA: Angels
http://www.studylight.org/dic/ebd/view.cgi?number=T240