spiritual energy is "formless" and takes on form when it needs a form (or physical vessel) through which to express "truth"
just as we, as spiritual energy, always existing always alive, take on a physical form to express some elemental truth
and our reincarnated selves are really art projects of the soul, one after another
so, too, do spiritual guides, angels, etc find a style and shape to "use" to speak to/with us
the way you see them is defined by the energetic "impulse" chosen as their mode of conveyance of an idea they wish to express to you as the "receiver" of that idea
you see a form because the energy has chosen to express "through form"
but, just like us in our physical "meat suits", the energy doesn't need a form to "exist"
it just chooses, in that moment, to express WITHIN FORM
my "two cents"