Summary: 1) The Shield of Faith (Ephesians 6:16) 2) The Helmet of Salvation (Ephesians 6:17a), 3) The Sword of the Spirit (Ephesians 6:17b)
John Bunyan, the author of Pilgrim’s Progress, wrote another famous allegory entitled The Holy War.... He believed that God and Satan are locked in a titanic war in which the souls of humanity are at stake — that we are the principal players in a real war. ... Bunyan sought, by the powerful use of allegory, to instruct believers in the subtleties of this warfare, and to reinforce the reality that every true believer is a warrior. Bunyan knew from Biblical revelation and repeated personal persecution that life is one long battlefield in which there can be no retreat, no surrender, and no quarter if we are to be faithful to Jesus Christ. It is significant that most of Bunyan’s work was done while in prison. The Christian soldier must never expect to find rest in this world. A believer will never hear orders to relax their guard or put their armor aside (Hughes, R. K. (1990). Ephesians: the mystery of the body of Christ (pp. 237–240). Wheaton, IL: Crossway Books.).
In Ephesians 6:14–17 Paul tells us of the seven pieces of armor with which God supplies His children to withstand the onslaughts of Satan and his hosts. We have seen the first three pieces of armor, specifically: 1) The Belt of Truth (Ephesians 6:14a) , 2) The Breastplate of Righteousness (Ephesians 6:14b), and 3) Feet prepared with the Gospel (Ephesians 6:15). We realized that we must be ready for battle, free of distractions, we must protect our mind and emotions guarded by God's righteousness and not our own and finally, we must stand on the truths of the Gospel, and rest in the peace it alone provides.
The first three pieces of amour: the belt, breastplate, and shoes (vv. 14–15)—were for long–range preparation and protection and were never taken off on the battlefield. The shield (Ephesians 6:17a), helmet (Ephesians 6:17a), and sword (Ephesians 6:17b), on the other hand, were kept in readiness for use when actual fighting began, hence the verb to take up.
1) The Shield of Faith (Ephesians 6:16)
Ephesians 6:16 In all circumstances take up the shield of faith, with which you can extinguish all the flaming darts of the evil one; (ESV)
Roman soldiers used several kinds of shields, but two were the most common. The first was a rather small round shield, perhaps two feet in diameter, that was secured to the arm by two leather straps. It was relatively lightweight and was used to parry the sword blows of one’s opponent in hand–to–hand fighting. The second kind was the thureos, to which Paul refers here. This shield was about two and half feet wide and four and a half feet high, designed to protect the entire body of the soldier—who was considerably smaller than the average man today. The shield was made of a solid piece of wood and was covered with metal or heavy oiled leather. Sculptured representations may be seen on Trajan’s column (Vincent, M. R. (1887). Word studies in the New Testament (Vol. 3, p. 409). New York: Charles Scribner’s Sons.)