Jamieson, Fausset and Brown on Ephesians 6:13

13. take ... of God--not "make," God has done that: you have only to "take up" and put it on. The Ephesians were familiar with the idea of the gods giving armor to mythical heroes: thus Paul's allusion would be appropriate.

the evil day--the day of Satan's special assaults (Ep 6:12, 16) in life and at the dying hour (compare Re 3:10). We must have our armor always on, to be ready against the evil day which may come at any moment, the war being perpetual (Psa 41:1, Margin).

done all--rather, "accomplished all things," namely, necessary to the fight, and becoming a good soldier.