What does Ephesians 6:13 mean?Because of the wide scope and power of spiritual evil faced by believers (Ephesians 6:12), Paul reminds Christians that all of these tools are critically important. God's armor is a package, not a cafeteria of items from which we can select. We must have salvation and God's Word. We need prayer and righteousness, not one or the other. All of these areas must work together to operate effectively.
Paul often groups interconnected spiritual ideas together to emphasize their importance. An example is his reference to the "fruit" of the Spirit, which mentions nine total attributes (Galatians 5:22–23). This is a literary technique, meant to imply that all listed areas are essential for the believer. This avoids the misinterpretation of picking and choosing which instructions a person wishes to pursue, while neglecting others.
Those who put on the full armor of God are promised certain benefits. The "evil day" can refer to any moment of spiritual attack. It does not refer to a future "last days" scenario. Believers are to constantly be on guard, living prepared with God's armor. Also, believers who wear God's armor can "stand firm," a phrase used in connection with success with God in the Old Testament (Exodus 14:13; 2 Chronicles 20:17; Psalm 89:28; Isaiah 46:8; Daniel 11:32).
As with verse 11, the phrases used in this verse strongly imply defense over offense. This is not to say that Christians are never called on to actively engage falsehoods (2 Corinthians 10:5). Rather, it is a reminder that in our spiritual battle, God will win the victory. We are not called on to charge against Satan, but to endure his attacks until Christ wins the ultimate triumph.