Watchman Nee

Anyone who serves God will discover sooner or later that the great hindrance to his work is not others but himself. He will discover that his outward man and his inward man are not in harmony, for both are tending toward opposite directions.

He will also sense the inability of his outward man to submit to the Spirit's control, thus rendering him incapable of obeying God's highest commands. He will quickly detect that the greatest difficulty lies in his outward man, for it hinders him from using his spirit.