Finally here means, “for the rest,” and shows that this section is built on what precedes it. Paul in essence was saying, “Based upon your glorious position in Christ (chapters 1–3) and in light of the worthy walk to which you are called (chapters 4–5, 6:1–9), I want to conclude by explaining to you the serious conflict in which your faith necessarily engages you.” In these verses Paul introduced the truth that the Ephesian believers could not only be strengthened by the person of the Lord, but also by His resources as they engaged in spiritual warfare. Many, if not all, had been worshipers of the Greek goddess Artemis prior to their conversion, and they had lived life dependent on her for their protection. But those days were now gone, and Paul told them to not bolster up strength from a false god, or from within themselves, but to be strong in the Lord and to put on the full armor of God.
The purpose of putting on God’s armor, for the Ephesians and for us, is to be able to stand strong in the Lord against the schemes of the Devil. We as believers are not told to advance against Satan, but only to “stand” and hold the territory of that which Christ and His body, the church, have conquered. The Devil’s schemes have been effective for thousands of years, so Paul urged the Ephesian believers to actively prepare, and put on the armor of God so they would not be defeated.