Ephesians 6:14-17 New International Version
“Stand firm then, with the belt of truth buckled around your waist, with the breastplate of righteousness in place, and with your feet fitted with the readiness that comes from the gospel of peace. In addition to all this, take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one. Take the helmet of salvation and the sword of the Spirit, which is the word of God.”
“The shield of faith is here compared to the great oblong shield, called a ‘Scutum’, which covered and protected the whole body. The shield of faith thus also covers all the other pieces of the armor of God, providing double protection.” 
The devil will try whatever means necessary to knock you off kilter faith-wise. He doesn’t fight fair. He studies you to find your weakest point and then attacks that point. The Lord is keenly aware of all that the devil does because when it comes to his children God dictates what the devil may inflict upon us. If God wasn’t aware and the orchestrator of all things then he would cease to be who he says he is in scripture.
The nature of the shield is to cover one’s entire body as described above. The shield provides double the protection against the wiles of our adversary, as it covers the underlying protection as well. Without armor and a shield for protection, we are painfully vulnerable. We mustn’t let our guard down for a moment. Be wary of tests and attacks. You must remember that you are the victor in all circumstances if you turn to God for guidance. You cannot fight this battle alone. Until next time, walk with the King and be a blessing!
 Taken from http://www.gladiatorsforgod.com/armour_05_shield.htm