“Take … the sword of the Spirit which is the word of God”. 

Eph 6:17 NIV 
Most modern soldiers attack with rifles or hand grenades. These are relatively new inventions but an indispensable part of the fighting man’s equipment. The only remnant of the ancient soldier’s attack weapon, the sword, is the bayonet which is only used in very close combat, if at all. 
Paul sees the need for the Christian to both attack as well as defend in the spiritual warfare with the devil. He saw the word of God as the most powerful instrument for the believer. He meant the words of Jesus, many of which were circulating informally in written form by the time Paul wrote. His bible would have been the Old Testament, from which he often quoted in his letters. The rest of the New Testament had not been written – or was in the process of being written. Some four hundred years elapsed before the books we know were declared by the church to be the New Testament. Note that it was not the Christian’s sword but the Spirit’s sword. Very early on the Christian community recognized these writings to have come from the work of the Holy Spirit through the apostles. To know them and to quote them was a vital part of the Christian’s constant effort to defend himself or herself against temptation. Jesus had done the same. 
The scriptures are also vitally important in evangelism. When you are talking to someone about the things of God to quote something Jesus said is to go right to the heart of what you are commending. It is well worth remembering a small but growing collection of verses and to be ready with them at any time. 

PRAYER THOUGHT Lord, help me to know and use the Bible effectively.