An Initial Response on Angels and Angelkin
An angel, regardless of the religion/s they may appear in, is probably best described as a spark struck off of the infinite consciousness of the Absolute, or (to be more local) a spark of the spark that is their origin-star, itself thrown off by the sudden birth/expansion of the universe. An angel is born/awakes into that primal light, and receives their essence from it, which is why some angels relate to other stars/universes as their "home" and some are more closely related to this solar system -- one of my own early names/titles was "Son of the Sun."
After that birth, which may be assumed as an extreme version of the idea of a "thought-form" being given complete life and soul, various paths are possible, including those of 'walk-ins', temporary full incarnations to fulfill a purpose/'assignment', guarding humans invisibly, merely appearing to serve a message or render assistance, or (though some angelkin will go as far as possible to avoid taking this seriously) fully entering the stream of rebirth with all its possibilities of 'being' other things and species as well, rather than just sheerly 'angelic-soul-in-(irrelevant/condescendi
Angels have an essentially energetic/light-formed body but are quite capable of taking on physical form, which can shift and alter according to intent or mood; generally, at least going from all the classical/ancient religious lore, they tend to manifest as young men of surpassing power and beauty combined, though this may be a preference attached to the cultural mores and prejudices of whatever human society they are making contact with. As such, they are fully capable of sexual intercourse with both material (human) and upper-energy level (fae) species, resulting in nephilim (scripturally, the superhuman/heroic mortal offspring of angels with human women) and some of the various tribes/types of elves. I do not believe they reproduce amongst themselves -- I myself was emanated fully-grown and conscious, with no 'cute little cherub' phase, so I surmise that genetic reproduction and inheritance is dependant upon an angel's either temporary or lifelong possession of a physical body infused with its physically-translated traits and potentials -- this could be combined with fae/elven heritage or be purely through the human bloodlines. They do have many traits in common with the fae as known, including the peculiar 'mortal' susceptibility to grief/despair as cited by Tolkien in his depictions of Elves -- emotional wounds are far keener than merely physical injuries, as they affect the entire energetic body, and are far more difficult to heal.
Based on their origin as sparks/aspects of the divine consciousness, each angel may be assumed to have an essential nature and central mission/'concept' that they follow and fight for -- which is the only ultimate constraint upon their free will, and which can be broken/reversed or perverted to extremes from its original idea. This is also the basic idea of angels being "messengers", as per Marshall McLuhan's famous declaration "The medium is the message" -- they are intermediaries of a specific nature or attitude towards the rest of "creation" that they oversee. Some angels (regardless of incarnation or state) have more distinctive and fierce natures than others, which is likely to be related to their ultimate age in the scheme of things -- I theorize that older angels have more primal and 'undiluted' essences to them, as compared to younger angels that have more connection to humanity's own various combinations of concepts and ideals since/as they evolved (cf. 'Angel of Protection' vs. 'Angel of Protecting Young Children from Emotional Bullying at School or on the Playground').
[Addendum (1/9/08) - On the other hand, an older angel is likely to have more mingled or clustered attributes, some of them not immediately understandable as part of the same nature -- as the 'generations' proceed, the concept of an angel's nature/mission seems to have become more and more specific, as well as to have become denoted as a mission/task rather than as an intrinsic instinct.]
They are also prone to be extremely idealistic, vehemently (and even dogmatically) philosophical, have grown a tad bureaucratic since my time (the Judeo-Christian kind, at least) and occasionally (make that frequently) are rather divisively "political" while amongst themselves...some recollection of this, from very early on in my findings, is detailed in my personal LJ post http://aureantes.livejournal.com/28627.h
At any rate, "God"/'Divine Command' is a contentious point....the Absolute that we (all of us) come from is generally as 'distant' to angels as they themselves tend to be to humans (even the sensitive kind), and the peculiar "political" nature of angels (as with humans) tends to come from their own convictions of knowing what "God" really wants...which may be benevolent, paternalistic, testing, guiding, merciful/comforting, enlightening/teaching, protective, preaching, 'morally prejudiced' or just plain wrathful and smitey at whatever they see as humans' sins and offenses.
I could say more in detail here, but there's a lot of personally-sensitive information in that area, as well as some further historical observations-&-corrections that are likely to strike quite a few people as blasphemous, even (and particularly) other angelkin of the traditional Christian persuasion. So I'll leave it at this load for the moment, take it for what you will, and will enlarge upon the personal content later within the private Anderen group on Yahell.