Angels are incapable of learning magic. We also have no great strength or stamina. I don't think we are any smarter than the average human, and certainly each of us has our own vices and failings.
We can die, although we do not die to old age.
In the end all we have on our side is time and planning, and a deep desire to make a difference in this world. To help humanity, somehow.
And yet every single day we come against beings whose power dwarfs ours. And every single day humanity pushes back, disobeys, and rejects our help, either through obstinacy or simple ignorance.
But we will help, every way we can, every day we can, for as long as there are any of us left.
Because a vow was taken. Because a God needs us to.
Because without that, what are we?
-Venerated teachings from the Highest of Angels