For our weapons of warfare are not carnal (of the flesh) but inherently powerful in God towards the destruction of strongholds while pulling down reasonings and every high thing exalting itself against the experiential knowledge of God and while bringing into captivity every thought unto the obedience of the Christ, – 2 Corinthians 10:4,5
Thoughts are not sin, but they lead to sin.
Therefore, we need to learn how to bring every thought into captivity.
Sin is exterior to the body – Everyone doing the sin also is doing the lawlessness, and the sin is the lawlessness – 1 John 3:4; Flee fornication. Every sin which perhaps a human does is exterior (outside of) to the body. But a fornicator sins against his own body – 1 Corinthians 6:18.
Thinking something bad does not make you sinful or unrighteous, until you accept that thought as something you are going to fulfill. Therefore, when a thought enters our mind we can, righteously, handle that thought and weight it against who we are in Christ. Does the desire match up with who you are in Christ? if not, reject it.
In Christ we live by grace, not under law, therefore we are free to live righteously. We are no longer bound to obey the enemy within (sin nature), Satan, or the world system.
Do not let your thought life convince you that you are anything other than who you are in Christ.
When we struggle with bad thoughts, we need to apply the defenses God has provided for us and bring every one of them into captivity so that they line up with who we are in Christ. This means, we consider each desire based upon how it will show forth who we are in Christ and glorify (show a proper opinion of ) God. If it won’t, we reject it because that is not who we are in Christ.
Don’t “do” the Christian life, “be” the person that you are in Christ. Remember, the Christian life is not about doing (live by law), it is about being (living out from grace) who we are in Christ.