[The decrees of God] are immutable and unalterable; they are the mountains of brass, out of which come forth the horses and chariots, the executioners of divine providence; signified by mountains, for their immoveableness, and by mountains of brass, for their greater stability and firmness (Zech. 6:1-8). The decrees of the Medes and Persians, when signed and sealed, were not to be changed or altered: but these are more unchangeable and unalterable than they were: we read of the immutability of the counsel of God, (Heb. 6:17) His purposes and decrees, which, like Himself, are the same today, yesterday, and for ever; without any variableness, or shadow of turning.
—John Gill, A Body of Doctrinal Divinity