Why was Moses' staff described in the verse as "as if it were a serpent" even though it had actually turned into a serpent?

The staff truly became a living being, as indicated by the verses, and it was not merely a simile. However, it was likened to a Jinn due to its swift movement, despite being a mighty serpent.

The "Jinn" refers to small snakes, while "thu'ban" (serpent) refers to large ones. So, it became a large snake, but was likened to a Jinn because of its swift movement.

Al-Zarkashi's statement in "Al-Burhan" confirms that the staff became a mighty serpent and was likened to a Jinn due to its shaking, movements, and swiftness.