The dictionary defines this as "the attribution of human characteristics to non-human beings, or things". It further states, "to represent (an abstraction) as a person; to be the embodiment of perfect example."
We know that corporeal mankind is not alone in the universe. Numerous interactions with spiritual and transdimesional realms and entities have been recorded, as has an overabundant history of evidence spanning centuries and cultures of the direct and visible personification of specific beings. Each culture, from pre-Neolithic, to New Age, has titled the visible form manifested by divine creative visualization for human-kind to behold and interact with. Flesh beings with flesh limitations often require a tangible form with which to relate; and the energies that inhabit less "material" dimensions know this. For the average mortal, with little or no psychic discernment, anthropomorphism is essential to the learning and understanding process. Humanity needs to brings its "deities" down to a comfortable level for interaction, and they are often found ready to accommodate us.
The personification of an entity lies in the realm of physics that mankind has not yet the ability to comprehend, let alone measure. Simply put, manifestation involves focused energy, transmuted into molecules that are shaped and densified into a humanly visible, and often tangible form. We already know that everything is comprised of energy molecules. The more dense their concentration, the more tangible the form. The more diffuse the composition, the less visible and tangible things become to our limited, human senses; and we have to really realize just how limited we are whilst sealed in this sack of clay.
All spiritual energy is originally formless, as once we all were. Take for example psychokenesis and telekenetic energy, where simple underdeveloped energy emissions can influence matter and movement. These things are already quite well documented. Imagine, for a moment, what mastery a highly evolved spiritual or transdimensional being can have over the energy that is its very life force! It can easily condense its molecular structure so that mortal eyes can perceive its densified form; and it can, with just as much ease, recreate a particular countenance so that humanity will readily recognize its function and intent.
While most humans do not have the ability (or perhaps, do not use the ability) to alter the laws of "known" physics, other entities do have that ability, (It would be arrogant for us to think that we know all there is to know about the physics of the universe, let alone transdimensional physics) These other entities use that ability to interact with the physical world. We have come to term such abilities, as metaphysics.