Behold, four chariots going forth - Alb.: “By the secret disposal of God into the theater of the world,” “from between two mountains of brass.” Both Jews and Christians have seen that the four chariots relate to the same four empires, as the visions in Daniel.
“The two mountains.” It may be that the imagery is from the two mountains on either side of the valley of Jehoshaphat, which Joel had spoken of as the place of God’s judgment, Joel 3:2, and Zechariah afterward Zechariah 14:4. It may then picture that the judgments go forth from God. Anyhow the powers, symbolized by the four chariots, are pictured as closed in on either side by these mountains, strong as brass, unsurmountable, undecaying, (Ribera), “that they should not go forth to other lands to conquer, until the time should come, fixed by the counsels of God, when the gates should be opened for their going forth.” The mountains of brass may signify the height of the Divine Wisdom ordering this, and the sublimity of the power which putteth them in operation; as the Psalmist says, “Thy righteousnesses are like the mountains of God” Psalms 36:6.