Ephesians 6:16

"In addition to all this, take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one." NIV translation

The previous pieces of armor were all put on and then they just did their thing but the shield is different. The shield must be picked up and carried and it reminds us that this battle takes some effort on our part. A shield is not only used for defensive purposes but can also be used to attack when in close. As believers, our shield is our faith in Jesus for salvation and provision. 

We know that we are God's chosen children and we know that He is faithful in caring for His children. Therefore, we know that "the evil one" can not overcome us.

Ephesians 6:17

"Take the helmet of salvation and the sword of the Spirit, which is the word of God." NIV translation

A helmet covers the head and protects the mind. The helmet of salvation speaks to the fact that we know that we are children of God and are saved. As we fight these spiritual battles, one of the favorite tactics of the devil is to try to get us to doubt our salvation but if we hold to our helmet we will not be affected by that tactic. We are also called to fight using the sword (word of God). Jesus gave us the example of this as He used the word of God to correct the devil when He was being tempted. (see Matthew 4)