The word angel is derived from the Greek word angelos, which means "messenger." Malakh, the Hebrew word for angel, also means messenger, and both words nicely coincide with the Persian word for angel, angaros, similarly meaning a courier.
The word "angel" can commonly be used to describe anyone who brings a message to another, whether a human being or a spirit. However, within some religions, angels are spirit messengers who bring messages of truth to aid mankind, while conversely, fallen angels bring forth messages of untruth to lead people astray and wreak havoc on Earth.
Angels are then traditionally believed to be supernatural beings who act as mediators between man and god. It is taught that angels have authority over the natural world, being organized into classes or heirarchies.
The origin of angels in history is quite complicated to figure out, due to angels or similar spirit beings being found within many cultures around the globe.
Angels are found within three key religions: Judaism, Christianity and Islam. Yet, angels, or divine helpers, were also found within Sumerian, Babylonian, Persian, Egyptian and Greek writings, as well, and played a major influence upon the ideas regarding angels within the key religions themselves. For example, it is well known that ancient Sumerian texts pre-dated the Hebrew book of Genesis, including the idea of the existence of angels. The Hebrew beliefs regarding angels were similarly shared with Christianity, and both Judaism's and Christianity's teachings of angels inspired the Islam beliefs concerning angels.
Though maybe called different names, benevolant spirit beings quite similar to angels can also be found within other religions, mythologies, and lore. Hinduism has avatars, Buddhism has devas and bodhisattvas, the Greeks wrote about daimons, and other spirit beings similar to angels, such as guardian spirits and spirit guides, have been taught by tribal cultures. All of these have similar function as helpful spirit messengers, or angels.
Today, many people believe in demons and that they are fallen angels. This teaching originated in the Hebrew text of Isaiah about Lucifer being cast out of heaven with one third of the angels following him to the Earth. When the text was written, Lucifer actually referred to a Babylonian king, but later Christian, albeit poetic, interpretation of the same text changed Lucifer into Satan, commonly believed by many now to be the "devil."
A common description sometimes given of angels is that they are "beings of light," which are sometimes described as "fearful to behold" due to their tall stature, purity, and sheer power. Some will also describe angels as having wings and maybe even halos. Yet, the western idea of wings and halos originated through ancient religions and mythology. Images of angels looking like human beings, but with wings, were an ancient idea that illustrated benevolant spirit beings as coming from a "higher place" or the "heavens." Wings were an easy way to convey the idea of angels crossing back and forth (or even up and down) from the spirit world to Earth and then back again. Many ancient gods were often depicted as birds or as having wings (think Egyptian, for example). By the fourth century (AD), angels were widely perceived as having wings within western cultures, while wings were virtually non-existent within the Eastern religions. Many ancient cultures had placed wings upon their deities, creatures and heroes, so it was natural for Christian artists to look to pagan cultures for inspiration. Christian artisans were inspired to add wings to angels by looking at Greek art. Muslim artists looked to Persian renderings as their inspiration for wings upon angels. During this same time, Christian painters also borrowed the idea of the halo from the Greeks and Romans who had used them prior. Today, most people with common sense can easily recognize that angels with wings and halos were an addition into religious art after much debate and eventual approval by the Roman Council of Nicaea after 325 AD.
However, many times in the bible, angels appear to be men and are described as such from Genesis (e.g. when Jacob wrestles an angel) to Revelation (e.g. the letters to each of the churches are addressed to the pastors, or angels of each church). Even the name given to the archangel Gabriel means, "Man of God." Furthermore, Jesus was attributed as teaching (in the gospel of Matthew) that during the resurrection, those raised would be "as" (or like) the angels of God in heaven. This statement is further clarified by the similar passage found in Luke 20 which states, "for they (the resurrected) are angelic." This very idea of the spirits of human beings after death being resurrected, or possibly "raised up" (spiritually speaking) as the spirit messengers we call angels, is echoed somewhat by the teachings of famed medium, Emanuel Swedenborg. Swedenborg called the spirits of dead humans, "angels," and claimed to visit with them often in the spirit world through trance states!
Today, many people look to angels for assistance or even intervention during crisis. A common modern-day description of angels are found in numerous stories of helpful, but mysterious strangers. These stories often tell of a person who seems to come to a person during a time of need, providing a word or help of some kind, then mysteriously disappearing quickly. During these experiences, the messenger or helper is indiscernable as an angel, but appears as a loving, caring human being. Similarly, spirits who come to comfort and lead dying people through the transition from this world unto the light (heaven, promised land, etc), are often described as angels, but are sometimes discovered to be deceased family members or friends of the one about to pass.
Thus, angels seem to have a very close association with humans, maybe even closer than we might think, when one examines biblical descriptions along with accounts of personal experiences. Summing up angels described within religion and within personal experiences as a whole, we know they are benevolant spirit beings that bring messages, aiding mankind; angels appear in human form; and angels have been described specifically as the spirits of humans within the spirit realm. Perhaps the term angels is a word to universally describe disembodied, yet enlightened spirits of humans, who help other human beings on both sides of the grave.