Notice in the next segment, take up the shield of faith, the part of the armor is named, but before it is named we are told that it is portable. The soldier must take it wherever he goes in case of attack and to show his army's strength to defend. Likewise, the Christian must "take up the shield of faith". Why? So he/she can "extinguish all the flaming arrows of the evil one."
The word "shield", spoken of by Paul in Ephesians 6:16, in the original Greek is thureos - meaning a large, door shaped shield. There are many different shields for many different combat situations, but this shield is the one the Holy Spirit impressed upon Paul to encourage believers to pray for. A total front covering shield.
A shield can be used as an offensive weapon at times. However, it is mainly used as a defensive weapon. When we apply the shield to our faith and call on faith to defend what we believe in - what does this mean? The original Greek word for "faith" in this verse is - pistis - "persuasion, that is, credence; moral conviction (of religious truth, or the truthfulness of God or a religious teacher), especially reliance upon Christ for salvation". Therefore, not only is there faith according to the Roman Road (confessing with your mouth "Jesus is Lord", believing in your heart that God raised Him from the dead and therefore being saved) but faith is also a personal persuasion, a blessed assurance of God seen throughout the hallmarks of one's life. Apologetics on a personal level.
The Shield of Faith becomes experiences in your life that you can draw from to combat a present threat by the enemy of your soul. For example if you and God have had a victorious experience over the spirit of depression and it decides to return - recall the victory and any details and your Shield of Faith will begin to "extinguish the flaming arrows of the evil one."
Now the challenge becomes to keep our Shield of Faith well maintained. In Paul's days, the Roman soldiers oiled their shield every morning whether in peace or at war. Because of the materials used back then the oil helped in keeping the shield more difficult to penetrate. A non-oiled shield dried up and could be broken easily with a sword or powerful arrow shot. Spiritually, believers need to keep the oil (The Word of God) applied to their lives and beliefs (Shield of Faith). If we do not do this we are easy, vulnerable targets for the evil spirits of our enemy - the devil.
So, yes there is a shield of faith to pray for, use, and maintain, but do not forget it is Your Shield Of Faith!