well, Christianity doesn’t “own” the concept of angels. the Hebrew Bible teems with angels. they’re prolific in the Qur’an and hadith (malāʾikah), made of light with “two, or three, or four” pairs of wings (Jibreel has six hundred, and his shape covers the whole horizon). and Zoroastrianism—more ancient by far—describes several classes of being: besides Ahura Mazda (the supreme being), there are Amesha Spentas (archangels), Arda Fravash (holy guardian angels), and the court of yazatas (angels). yazatas are worthy of worship, while daevas (devils) should be rejected. (and there were winged gods before there were angels: the Egyptian god Horus, depicted as a winged disc; Hermes, the messenger-god; Eros; Nike, “the winged goddess of victory”, is called angelos in some texts, and her adoption by the Romans heavily influenced later angelic images.)
you can write about angels apart from the Christian God, but I doubt you could write about them apart from divinity—at least, I don’t know of any narrative which manages to transmute angels into secular creatures.
broadly speaking, angels are monsters—and might be the quintessential monster because the word derives from Latin monere, “to show” / “to warn”, and angels are essentially bearers of revelation. “angel” is rooted in the Greek ἄγγελος, “messenger”, chosen translation of Biblical Hebrew מַלְאָךְ, “one who is sent (with a message)”—with the morphological implication of a tool or a means of carrying out.
in just about every tradition, angels exist in close relation to god (though not coeternal with him, c.f. 13th century theology on “aeviternity” of angels). they explicitly depend on a creator in a way that most monsters don’t: angels are about God, about the ways and forms in which a god reveals itself to humankind—the articulation of mercy, judgement, knowledge, glory. the awe and terror of the divine. the gulf and the bridge between divinity and humanity (and endless debates after Aquinas about angelic free will). the concept of angels draws together a long rich complex history of religious writing and iconography across many cultures. trying to scrape that out and render it a tabula rasa would be like telling your reader not to think of an elephant. but the divinity that angels describe is, from a storytelling point of view, up to you.