“O wretched man that I am! who shall deliver me from the body of this death? I thank God through Jesus Christ our Lord. So then with the mind I myself serve the law of God; but with the flesh the law of sin.” (Romans 7:24-25)
Wretched and miserable man is God's commentary on human nature, yet, this very nature with all of its vile passions and desires is what many Christians rely upon for counsel as they echo the world's poisonous philosophy of Let your heart be your guide! The answer to the entire discussion lies within the last verse. As in everything, the Lord Jesus Christ is the answer. His Spirit has rendered the old man's power ineffective, and though the old man is still present, he is no match for the finished work of Christ.
Sanctification is positional in Jesus Christ upon the moment of salvation (I Corinthians 1:2), yet practically, it is a life-long work (II Corinthians 3:18). Let every believer remember that his flesh is entirely opposed to this ongoing work, and will resist it in every way with ferocious tenacity.