An angel, especially according to Abrahamic religions and Zoroastrianism, is a spiritual being superior to humans in power and intelligence. Angels are typically described as benevolent, dreadful, and endowed with wisdom and knowledge of earthly events, but not infallible; for they strive with each other, and God has to make peace between them. Most of them serve either as intermediaries between Heaven and Earth, or as guardian spirits. They are studied in the theological doctrine of angelology. In Christian Science, the word "angel" is used to refer to an inspiration from God. The use of the term has extended to refer to artistic depictions of the beings, and it is also used figuratively to refer to messengers and harbingers, and to people who possess high qualities of goodness, purity, selflessness, intelligence, and/or beauty.