In addition to all this, take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one. (Ephesians 6:16 NIV)
Paul has talked about personal protection such as the breastplate and having the proper shoes to stand firm. Now he is adding a shield. A Roman shield was made of wood covered with leather. It was about four feet by two and a half. It was large enough to cover the main parts of the body. It would deflect any flaming arrows that came from the enemy. Paul calls the spiritual shield, Faith. Faith does two things. It gives us the strength to stand firm and resist what Satan throws at us. Faith also gives us trust knowing that God is in control and He has our back, our front, and everything about us. We can go forward for Christ because we have Faith in His leading.
for everyone born of God overcomes the world. This is the victory that has overcome the world, even our faith. (1 John 5:4 NIV)
And without faith it is impossible to please God, because anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him. (Hebrews 11:6 NIV)