What do you mean when you say, "we must adopt a new nature"? How do we do that?
Much love!
Look at it like this. You can take one of two choices.
1) Choose to carry about with a carnal mentality, coveting, lusting, hating, etc. and still do a few good deeds. Or, you can...
2) Choose to live under the lordship of Christ all the time, which requires us to have our entire nature converted from carnal to spiritual. This doesn't make us perfect, but it allows God to invest His power in us so that we overcome sins.
All men can overcome their sin tendency, when they choose to obey God in their conscience and do good. The problem is that men are satisfied with just doing isolated good deeds, only to return to their carnal, selfish nature. Wanting our own way, we lose God's power to overcome sin, and become enslaved by the sin nature.
To get completely free from the power of sin we must turn our lives over completely to Christ, to be endowed with a new nature--some call it being "born again." I just call it embracing the New Nature Christ wants us to have. It is the need to live in constant fellowship with God. He doesn't want us some of the time. He wants us all of the time. I'm happy to oblige Him!
I'm sure you are too. I appreciate your good spirit, brother. I know I say things that make you suspicious. But bear with me. I'm open to whatever the Lord wants in my life.