Grace

Grace is celestial energy integral to angels. It is essentially what differentiates an angel and a human. If an angel removes their grace, they are either rendered mortal within their vessel, or, if they are not using a vessel, are reborn to human parents in their own body.

Grace gives angels access to Enochian magic, which is how they use their abilities. Without it, they are rendered almost completely human.

Overview
Grace is a type of energy angels are infused with. It resembles a shining bluish-white mist.

It appears that all angels are endowed with their own grace. This includes not only average angels such as Joshua and Theo but also seraphim such as Nathaniel. Therefore, it can be assumed that other types of angels, e.g. Cupids and archangels, also have grace. When not infused in an angel, grace must be stored in a vial or it will fall to Earth. Humans who see falling grace may mistake it for a meteorite. Where grace touches down on Earth, it vastly enriches its surroundings rather than destroys them; the presence of Anael's grace caused a barren field to flourish with vegetation and the spot where it landed created a massive oak tree that looked as though it were centuries old in the space of six months.

Grace is the source of most of angels' power, endowing them with Enochian magic, including immortality and teleportation. However, angels who had their grace removed may still be able to tap into varying powers, including the ability to tune into "angel radio", Supernatural Perception, and telekinesis.

So long as a vessel is possessed by an angel, that vessel also contains that angel's grace. Even after an angel departs from their vessel, a portion of their grace lingers within that vessel. Containing traces of an angel's grace does not harm the human in question and may even help them.

The archangel Gabriel confirms that an archangel's grace will recharge.

Removal
Though it is agonizing for the angel, it is possible for an angel's grace to be removed, either voluntarily or by force and in either vessels or in their true forms. It is viewed as a serious crime for angels to remove their own grace, one that requires the angel in question to be punished either via execution or imprisonment and torture.

Angels who lose their grace fall to Earth and essentially become humans. If the angel in question is possessing a vessel at the time they lose their grace, they are then locked into their vessel until death. If, however, the angel does not have a vessel, they are reborn to human parents through a human body of their own. Angels who lose their grace become subject to human emotions, urges, and weaknesses. Other angels may still recognize an angel who has lost their grace, but will be able to tell that they are no longer truly an angel.

It is also possible for angels who have lost their grace to regain it in order to restore their angelic power and status. They can use either their own grace (if they can find it) or remove the grace of another angel and use it for themselves. The effects of an angel absorbing another angel's grace are unknown—specifically, whether the angel regains all of his original powers or that of the other angel's. However, its revealed that using another angels grace for too long will cause the grace to burn out and kill the angel in question, although the exact timeline is unknown. Whether or not any other creature can also absorb grace is also unknown. The absorption of grace is a potentially dangerous process for humans and demons.

Angels who were rendered mortal have shown some supernatural abilities, most commonly being the ability to hear other angels' telepathic communications, colloquially known as "angel radio".