The horse is prepared for the day of battle

These words can be translated in active form. AT: "Soldiers prepare horses for the day of battle" (See: rc://en/ta/man/translate/figs-activepassive)

the day of battle

The word "day" refers to time that may be longer or shorter than a day. AT: "when there is a battle" (See: rc://en/ta/man/translate/figs-idiom)