The piece of armor known as the "sword of the Spirit" is the only piece of armor that has the ability to cut, wound, and hurt our enemy, the devil. It's not the Bible lying on the coffee table that makes the enemy flee, but it is the Word of God hidden in our heart, activated by the power of the Holy Spirit, and spoken in the right situation. It's similar to what is spoken when Jesus said in John 6:63, that "...the words that I speak unto you, they are spirit and they are life." The Word by itself doesn't make us free. It is the Word we know and speak that will deliver us (John 8:32).
Why is the Word so effective? It's because it is the WORD of God. It has authority, because it is the WORD of God. God's Word above all authority of the church, of reason, of intellect, and even of Satan himself.
It is the Holy Spirit that wields this Word as it is spoken in faith. Speaking God's Word in faith brings the Holy Spirit into action. In Luke 4, when Jesus was tempted of the devil for forty days, it was the Word of God, that Jesus used to defeat the enemy in the time of His temptation. Jesus constantly met His temptation by quoting from God's Word as He repeatedly stated the phrase, "It is written."
The Christian must avail himself of God's Word by placing it in his heart, so that the Holy Spirit may bring it forth at the right times to accomplish a complete and total victory. It's ours!