It is the work of the souls who return from the earth to communicate with the earth very often, and it is such angels who are generally known to man. Angels who have never manifested as men on earth, only experience life on earth by the medium of other minds and bodies, which by their evolution come closer to the angelic heavens. They take these as their instruments, and at times reflect themselves in them, and at times have them reflected in themselves. This is not obsession, but inspiration.