2 Corinthians 5
3 "For though we walk in the flesh, we do not war after the flesh:
4 (For the weapons of our warfare are not carnal, but mighty through God to the pulling down of strong holds;)
5 Casting down imaginations, and every high thing that exalteth itself against the knowledge of God, and bringing into captivity every thought to the obedience of Christ;"
One of the big areas of spiritual battle in this life is in our minds, our thoughts.
We must learn to take every thought into captivity for obedience to Christ.
Our thoughts come from many sources. Our thoughts can come from what our parents said to us, either as a child or as an adult. Parental pronouncements can have a huge impact on our view of ourselves, rooted deeply in our emotions thus increasing the influence they can have on our opinion and view of ourselves.
Similarly, friends or acquaintances from our daily life can say things to us or about us that have a huge impact on how we see ourselves.
Furthermore, in many ways ideas are promoted which may or may not be true, but said enough times, can tend to influence our opinions about ourselves, our world, our circumstances, etc.
The Bible also reveals that the devil himself can speak to us and plant ideas in us that are destructive and deceptive, seeking to cause us harm.
In addition to all of this, our flesh, our pride, our desires, and even sins such as jealousy, envy, selfish ambition, and fear can influence what we think and say and do.
Because of these many sources of potentially false and destructive thoughts and ideas, we must learn to cast down imaginations and every high thing that exalts itself against the knowledge of God, and take every thought captive for obedience to Christ.