What it means

For though we live in the flesh, we do not wage war according to the flesh. The weapons of our warfare are not the weapons of the world. Instead, they have divine power to demolish strongholds. We tear down arguments and every presumption set up against the knowledge of God; and we take captive every thought to make it obedient to Christ.

From 2 Corinthians. Read the verses around it when you can.