Harness the horses; and get up, ye horsemen, and stand forth with your helmets; furbish the spears, and put on the brigandines.
Harness the horses - namely, to the war-chariots, for which Egypt was famed (Exodus 14:7; Exodus 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.