It must be understood that prime matter, and form as well, is neither generated nor corrupted, because every generation is from something to something. Now that from which generation proceeds is matter, and that to which it proceeds is form. So that, if matter or form were generated, there would be a matter for matter and a form for form, endlessly. Whence, there is generation only of the composite, properly speaking.
Thomas AquinasA person is disposed to an act of choice by an angel ... in two ways. Sometimes, a man's understanding is enlightened by an angel to know what is good, but it is not instructed as to the reason why ... But sometimes he is instructed by angelic illumination, both that this act is good and as to the reason why it is good.
Thomas Aquinas