They become angels when they are sent. For the name angel refers to their office, not their nature. St. Augustine Angels are students in Heaven and teachers on Earth. Angels are the gatekeepers to the soul. Angels are very down to earth.
Angels believe in miracles.
I say Angels ARE Miracles. Chesterton Angels can fly even though they are well grounded. Angels can't read music, they wing it. Angels come in all shapes, sizes and colors. Angels don't make too much noise when they flap their wings.