4. Harness the horses—namely, to the war chariots, for which Egypt was famed (Ex 14:7; 15:4).
get up, ye horsemen—get up into the chariots. Maurer, because of the parallel "horses," translates, "Mount the steeds." But it is rather describing the successive steps in equipping the war chariots; first harness the horses to them, then let the horsemen mount them.
brigandines—cuirasses, or coats of mail.