Stand therefore, having your loins girt about with truth, and having on the breastplate of righteousness; And your feet shod with the preparation of the gospel of peace; Above all, taking the shield of faith, wherewith ye shall be able to quench all the fiery darts of the wicked. And take the helmet of salvation, and the sword of the Spirit, which is the word of God: Ephesians 6:14-17
"In verses 14b-17, Paul deals with the pieces of the armor. Every small reference is a quotation or a reference from the Old Testament. In other words, the way we resist Satan is by means of Scripture. Every piece concerns Scripture and every piece is somehow related to the positional truth of the believer.
First, there is the girdle of truth. This comes from Isaiah 11:5. The girdle was bound around for three reasons: first, to allow for freedom of movement; secondly, it was used to carry weapons; and thirdly, it was used to display things outwardly. The meaning of this is truthfulness and sincerity based upon Scripture.
The second piece of armor is the breastplate of righteousness. This is taken from Isaiah 59:17 and it protected the vital organs. In relation to spiritual warfare, this refers to the imputed righteousness of the Messiah or positional righteousness, and also daily righteousness or practical righteousness.
The third piece of armor is ‘shoes’ of the gospel of peace. This is taken from Isaiah 52:7; Nahum 1:15. The emphasis here is on walking. The meaning is secure footing on a sure foundation which, of course, is the Messiah and His Word.
The fourth piece of armor is the shield of faith. The purpose of the shield is to cover the whole body. It is to be used against the darts of the devil. The faith mentioned here is the principle by which we resist.
The fifth piece is the helmet of salvation. This is taken from Isaiah 59:17. This is the assurance of salvation in spiritual warfare.
The sixth piece of armor is the sword of the Spirit. This is the only offensive weapon, the others are all defensive. The sword of the Spirit is the entire, written word of God."
Each of the types of armor mentioned in Ephesians six are terms taken right out of the Old Testament.
And the main point Paul is making is that the Scriptures are the key to victory in terms of spiritual warfare. This entails learning the Scriptures well, studying them as a whole to have a comprehensive knowledge of “the whole counsel of God.”
Second, it involves applying the Scriptures to our daily lives. A third principle is to deal with specific life issues by looking up passages (using a concordance or other study tool) that directly address these issues – studying, memorizing and using such verses to resist Satan.
When Jesus was tempted three times, He resisted each by quoting Scripture directly relevant to each temptation. Obviously, He needed to know the Scriptures in order to do this. And this is exactly what Paul means when he urges his readers to put on the armor of God.