Angels are spirits, but it is not because they are spirits that they are angels. They become angels when they are sent. For the name angel refers to their office, not their nature. You ask the name of this nature, it is spirit; you ask its office, it is that of an Angel, which is a messenger.
The real accomplishment of modern science and technology consists in taking ordinary men, informing them narrowly and deeply and then, through appropriate organization, arranging to have their knowledge combined with that of other specialized but equally ordinary men. This dispenses with the need for genius. The resulting performance, though less inspiring, is far more predictable.