Charles Hodge on Ephesians 6:13

V. 13. Wherefore, i. e. because you have such formidable enemies, and because the conflict is inevitable, ἀναλάβετε τὴν πανοπλίαν τοῦ Θεοῦ, not only arm yourselves, but take the panoply of God; no other is adequate to the emergency. Ἵνα δυνηθῆτε ἀντιστῆναι ἐν τῇ ἡμέρᾷ τῇ πονηρᾷ, in order that ye may be able to withstand, i. e. successfully to resist, in the evil day. The evil day is the day of trial. Ps. 41, 2, "The Lord will deliver him in the time of trouble;" or as it is in the Sept. ἐν ἡμερᾷ πονηρᾷ; and Ps. 49, 5, " Wherefore should I fear in the days of evil;" Sept. ἐν ἡμερᾷ πονηρᾷ. The day here referred to is the definite day when the enemies previously mentioned shall make their assault. This however is not to be understood with special, much less with exclusive, reference to the last great conflict with the powers of darkness which is to take place before the second advent. The whole exhortation has reference to the present duty of believers. They are at once to assume their armour, and be always prepared for the attacks of their formidable enemies.

Καὶ ἅπαντα κατεργασάμενοι στῆναι, and having done all to stand. This is understood by many to refer to the preparation for conflict. Having made every preparation, stand ready for the assault. But that idea is included in the former part of the verse. Others take κατεργάζεσθαι in the sense of debellare, vincere; having overcome all opposition, or conquered all, stand. The ordinary sense of the word includes that idea. ‘Having done all that pertains to the combat, to stand;’ i. e. That you may be able, after the conflict is over, to maintain your ground as victors.