Spirit

Eph. 6:17 (NKJV)

And take the helmet of salvation, and the sword of the Spirit, which is the word of God;

There are two natural instincts when one is under attack, fight and flight. When we are in a dangerous situation our body produces adrenalin to give us the strength to take either of those options. In a spiritual sense, God has placed in us His Spirit to bring to mind verses of scripture to be used as a weapon against Satan. It is most vividly seen in Matthew 4, as Jesus quotes scripture to fight off temptation in the wilderness. So what should we do? We should memorize scripture. Hide God's Word in our hearts so that we might not sin against Him. The more we know of God's Word, the better equipped we will be for spiritual warfare. Bible memorization is not for kids anymore!