An angel is, in many religious traditions, a lesser spiritual being which assists and serves God or the gods. The word originally comes from the Latin angelus, itself derived from the Greek ángelos, meaning "messenger". The closest Hebrew word for angel is malach, meaning messenger.
Angels appear in several Old Testament stories, such as the warning to Lot of the imminent destruction of Sodom. Many Old Testament chapters mention an "angry God" who sends His angel to smite the enemies of the Israelites. Traditional Jewish biblical commentators have a variety of ways of explaining what an angel is. The earliest Biblical books present angels as heavenly beings created by God, some of whom apparently are endowed with free will. Later biblical books in the Tanach present a stunningly different view of angels, such as in the book of Ezekiel, and these angels bear no relation whatsoever to the popular understanding of what an angel is.
In the medieval era, Judaism developed a rationalist view of angels that is still accepted by many Jews today. The rationalist view of angels, as held by Maimonides, Gersonides, Samuel Ibn Tibbon, etc., states that God's actions are never mediated by a violation of the laws of nature. Rather, all such interaction are by way of angels. Even this can be highly misleading: Maimonides harshly states that the average person's understanding of the term "angel" is ignorant in the extreme. Instead, he says, the wise man sees that what the Bible and Talmud refer to as "angels" are actually metaphors for the various laws of nature, or the principlies by which the physical universe operates, or kinds of platonic eternal forms. This is explained in his "Guide of the Perplexed" II:4 and II:6.
II:4 "...This leads Aristotle in turn to the demonstrated fact that God, glory and majesty to Him, does not do things by direct contact. God burns things by means of fire; fire is moved by the motion of the sphere; the sphere is moved by means of a disembodied intellect, these intellects being the "angels which are near to Him," through whose mediation the spheres [planets] move....thus totally disembodied minds exist which emanate from God and are the intermediaries between God and all the bodies [objects] here in this world."
II:6 "...Aristotle's doctrine that these disembodied spheres serve as the nexus between God and existence, by whose mediation the sphere are brought into motion, which is the cause of all becoming, is the express import of all the Scriptures. For you will never in Scripture any activity done by God except through an angel. And "angel", as you know, means messenger. Thus anything which executes a command is an angel. So the motions of living beings, even those that are inarticulate, are said explicitly by Scripture to be due to angels.
...Our argument here is concerned solely with those "angels" which are disembodied intellects. For our Bible is not unaware that God governs this existence through the mediation of angles...(Maimonides then quotes discussions of angels from Genesis, Plato, and Midrash Bereshit Rabbah)...the import in all these texts is not - as a primitive mentality would suppose - to suggest any discussion or planning or seeking of advice on God's part. How could the Creator receive aid from the object of his creation? The real import of all is to proclaim that existence - including particular individuals and even the formation of the parts of animals such as they are - is brought about entirely through the mediation of angels.
For all forces are angels! How blind, how perniciously blind are the naive?! If you told someone who purports to be a sage of Israel that the Deity sends an angel who enters a woman's womb and there forms an embryo, he would think this a miracle and accept it as a mark of the majesty and power of the Deity - despite the fact that he believes an angle to be a body of fire one third the size of the entire world. All this, he thinks, is possible for God. But if you tell him that God placed in the sperm the power of forming and demarcating these organs, and that this is the angel, or that all forms are produced by the Active Intellect - that here is the angel, the "vice-regent of the world" constantly mentioned by the sages - then he will recoil. For he [the naive person] does not understand that the true majesty and power are in the bringing into being of forces which are active in a thing although they cannot be perceived by the senses.
The sages of blessed memory state clearly - to those who are wise themselves - that every bodily power (not to mention forces at large in the world) is an angel and that a given power has one effect and no more. It says in Midrash Bereshit Rabbah "We are given to understand that no angel performs two missions, nor do two angels perform one mission." - which is just the case with all forces. To confirm the conclusion that individual physical and psychological forces are called "angels", there is the dictum of the sages, in a number of places, ultimately derived from Bereshit Rabbah, "Each day the Holy One creates a band of angels who sing their song before him and go their way." [[[Midrash]] Bereshit Rabbah, LXXVIII] When this midrash was countered with another which suggests that angels are permanent...the answer given was that some are permanent and other perish. And this is in fact the case. Particular forces come to be and pass away in constant succession; the species of such forces, however, are stable and enduring....[Giving a few more examples of the mention of angels in rabbinic writings, Maimonides says] Thus the Sages reveal to the aware that the imaginative faculty is also called an angel; and the mind is called a cherub. How beautiful this will appear to the sophisticated mind - and how disturbing to the primitive."
- Readers whose understanding of Maimonides is coloured by Orthodox interpretations of Judaism are thunderstruck - and may even be angered - when confronted by these passages, for they are a rejection of the classical Jewish view of miracles; they substitute a rationalism that seems more appropriate for 20th and 21st century religious rationalists
Angels are frequently depicted as human in appearance, though many theologians have argued that they have no physical existence. (Hence the frequently recounted tale of Scholastics arguing about how many angels could fit on a pinhead; if angels possess physical bodies, the answer is "a finite number", if they do not, the answer is "an infinite number".) Seraphim are often depicted as 6 wings radiating from a center either concealing a body or without a body.
Some Christian traditions hold that there are as many as ten classes of angels; this is particularly clear in the work of Pseudo-Dionysius the Areopagite, an unknown fifth century author whose work The Celestial Hierarchy gives the names that have become part of tradition: angels, archangels, principalities, powers, virtues, dominions, thrones, cherubim, and seraphim.
Some medieval Christian philosophers were influenced by the views of Maimonides, and accepted his view of angels. Today, these views of angels are still technically acceptable within many mainstream Christian denominations. However, for all practical purposes most Christian laypeople know little or nothing of these views, and do not accept them.