"Therefore put to death your members which are on earth: fornication, uncleanness, passion, evil desire, and covetousness, which is idolatry." Colossians 3:5 Through the sacrifice of Christ on the cross, a person has the ability to gain something that was unattainable before and has been hidden as a mystery for ages: a new heart. The veil has been torn (Mark 15:38, 2 Cor. 3:14-16), so a person is able to put to death the members which are earthly - fleshly. A person can, by faith, leave the old on the cross and put on the new, the new heart and the new clothing of righteousness in the spirit. "Do not lie to one another, since you have put off the old man with his deeds, and have put on the new man who is renewed in knowledge according to the image of Him who created him." Colossians 3:9-10
I always found it interesting, why the Bible is split into two, why there is an Old Testament and a New Testament. Behind these testaments, stand a covenant. I like to think of these covenants as being a model for our relationship to God. In what position are we in relationship to God. It is important to understand these models and how they are different.