We know that our old (unrenewed) self was nailed to the cross with Him in order that [our] body [which is the instrument] of sin might be made ineffective and inactive for evil, that we might no longer be the slaves of sin.
Once you receive Christ as your Savior the old sinful nature of your spirit man has been done away with, as your spirit man has been made new. There is as the above scripture reveals, an old unrenewed nature, which has to do with the soul (mind, will, and emotions), that James 1:21 tells us must be saved (delivered) from the old natures ways by receiving with meekness the implanted Word of God.
It is this renewal of the mind that helps us to develop our spirit man, and in doing so this new man leads you in victory over the flesh. For the mind to be renewed you must receive the Word with meekness (complete humility). Simply put, you don’t question, argue with, nor doubt God’s Word. This means you simply believe what it says and act upon it.
As James chapter one goes on to tell us, one who is a hearer of the Word but not a doer deceives themselves. But a doer of the Word will be blessed in what they do. One’s mind is not fully renewed until they begin to act upon the Word of God. Take God at His Word. Accept everything it says you as a born again child of God are. The more you allow His Word to change your way of thinking, the more it will change the way you live, no longer a slave of sin.