This word is defined in verse 5, "We are destroying speculations and every lofty thing raised up against the knowledge of God, and we are taking every thought captive to the obedience of Christ" (emphasis mine). These two verses are part of an evangelistic context. It is one of the greatest passages that teaches us what it is we do when we witness to unbelievers. Paul says earlier in the chapter that Christians war not against the flesh, but against Satan for the minds of men and women who are lost. They have found, according to verse 5, refuge in lies that originate from the Father of Lies. These lies, expressed in philosophical world views, have become a safe haven for people, who look to them for their identity and comfort and meaning and purpose in life. They have been duped into thinking that they may rest secure in their own individual belief systems. Remember, Satan works on the minds of people.

Now Paul uses an interesting word to describe these false belief systems. Our English Bibles translate is "fortresses", because these false views have become just that to the unbeliever. What is interesting about the Greek word behind this translation is that it is also the same word for "prison". While "fortresses" or "strongholds" is the better translation in this context, one can’t help but wonder if there is intentional irony here—people who reject the truth and embrace error have not protected themselves; they have imprisoned themselves—locked away for the day of judgment. By using a word that has two meanings, Paul sounds a note of urgency to us to be about the business of tearing down the walls of these fortresses, because they are not the safe havens that people think they are. Rather, they are nothing but prisons.

Don’t miss the strong language Paul uses to describe the work of evangelism. It is war. Christians fight for the minds of individuals, to set the prisoners free. We are taking their thoughts captive for Christ. The weapon we use to wage war against these supernatural strongholds in which people have entombed themselves is not conventional. It must also be supernatural. It is specifically the Word of God. It is with biblical truth that we use to chip away at the walls of the unbeliever’s belief system and challenge his thinking. We must play the critic and help him to see just how foolish his error is and, at the same time, how vital the biblical world view is. It is in this altercation that God changes the pagan heart and saves him.