One detail I kept coming back to while researching Sephiroth is his name.
“Sephiroth” comes from sefirot, the plural of sefirah in Kabbalah, referring to the ten emanations through which the divine is expressed in the Tree of Life. The connection becomes particularly fitting by the end of Final Fantasy VII, when Sephiroth is no longer presented simply as a legendary SOLDIER. He is literally staging an ascension: sitting at the center of the Planet’s wound, absorbing its energy, and attempting to place himself above humanity.
And then the game gives him an angelic final form.
That does not mean every detail of Safer Sephiroth is a direct Kabbalistic reference. FFVII mixes religious imagery very freely. But the progression is hard to ignore: a man named after a concept associated with divine emanation eventually transforms himself into something designed to look like a false celestial being.