The exhortations here come to the church as a whole to stand fast in the panoply that God supplies in Christ. Individuals partake but are not isolated and on their own. The members of Christ’s united people are clothed with Christ in whom is all truth (Eph. 4:21). They stand their ground clothed in truth (6:14) and speak the truth to one another (4:25), maturing together to Christ’s stature produced by the Word of God and its instruction (vv. 7–16; 6:17).
The strength upholding the church in its conflict flows out of Christ’s supremacy over every competing realm and power that can be named both in this age and in the next (e.g., Eph. 1:15–23; 4:10). Hence, Christians are to “be strong in the Lord and in the strength of his might” (6:10, emphasis added; see 3:7, 16, 20) and are urged to be “strengthened with all power, according to his glorious might, for all endurance and patience with joy” (Col. 1:11).
Being told to put on the Lord’s armor may sound like David attempting to put on Goliath’s armor (1 Sam. 17:5–6). It’s so big and we’re so little. There are two things that help us.
First, putting on the armor of God that Christ Himself bore is tantamount to putting “on Christ,” which we have already done when we were baptized “into Him” (Rom. 6:3 ; Gal. 3:27). This is tantamount to telling us to look to Christ in faith for all things. Notice the parallels in this passage:
The night is far gone; the day is at hand. So then let us cast off the works of darkness and put on the armor of light. Let us walk properly as in the daytime, not in orgies and drunkenness, not in sexual immorality and sensuality, not in quarreling and jealousy. But put on the Lord Jesus Christ, and make no provision for the flesh, to gratify its desires. (Rom 13:12–4, emphasis added)
Our faith in Christ informs everything about our daily lives so that we can stand firm in steadily sanctified holy array.
Second, Paul’s exhortation is summarized in Ephesians 6:18–20, where he tells us to pray “in the Spirit” (v. 18). This is how we wield the “sword of the Spirit”: prayer. We are under orders from the Prince of Peace (Isa. 9:6; Eph. 2:14–17), and our only offensive weapons for conquest of the world are prayer and the “word of God” (v. 17), which centers on glad tidings of peace (vv. 15, 19–20) and love. Like a tiny science-fiction weapon that can destroy a star, gospel proclamation soaked in prayer packs a huge wallop: “For the weapons of our warfare are not of the flesh but have divine power to destroy strongholds” (2 Cor. 10:4).