Christians should use the protective resources God gives them in fighting the devil in the same way a soldier puts on armor to protect himself against his enemies. (See: [[rc://en/ta/man/translate/figs-metaphor]])
The words "stand" and "stand firm" represent successfully resisting or fighting something. Alternate translation: "so that you may be able to resist evil ... to remain strong" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here the word "day" can refer to any short period of time, even a period longer than a day. Alternate translation: "at the evil time" or "when people do evil deeds" (See: [[rc://en/ta/man/translate/figs-synecdoche]])