In addition to all, taking up the shield of faith with which you will be able to extinguish all the flaming arrows of the evil one. -Ephesians 6:16 NASB
The shield was in a sense, a wall of protection for a single soldier out in the open to cover himself from deadly arrows. When the soldiers were all together, they lined up tight and made up a wall with a roof—the shields being above the soldiers, overlapping shield with shield making a link all the way to the back protecting the men from arrows hitting them from above.
The arrows of the enemy are doused with a flammable tar, which is lit on fire to cause extreme or optimal damage to the target. The shield keeps the arrows away from the soldier and even turns it off—not allowing the fire to spread by hitting its target and eventually dies off.
As Christians, our faith is our shield that protects us from the front and from the top—keeping the enemy from hitting us. The arrows are doused with all types of deception for the sole purpose of destroying our faith in Jesus Christ. Without strong faith, we will get hit, but the question becomes, how bad would that hit be? We strengthen our faith by reading the Word of God with prayer—doing what it says.