The idiom "从天而降" is formed through a classical Chinese grammatical structure that literally translates to "from sky and descend," meaning "to descend from the heavens." It breaks down as: 从 (cóng, "from"), 天 (tiān, "sky/heaven"), 而 (ér, a classical grammatical particle connecting the manner or direction), and 降 (jiàng, "to descend/fall"). The phrase employs 而 as a connective to link the prepositional phrase "从天" ("from the sky") with the verb "降," describing the action's origin and manner. Figuratively, it describes something or someone appearing suddenly and unexpectedly, as if falling from the sky, and has been lexicalized as a set four-character idiom expressing sudden, unforeseen arrival.