I was reading a testimonial article in Christianity Today (December 2016) written by a man who became addicted to pain pills. He writes on p. 39:
"I've realized that the word 'addict' is a particularly useful descriptor for who I have always been. I always resonated with Paul's lament: ' I do not the good I want to do, but the evil I do not want to do--this I keep on doing' (Rom. 7:19)
"Some who have never experienced the furious grip of chemical dependence are tempted to split the world into 'addicts' and 'non-addicts,' morally bad and morally good. As I've said, I did not realize how fully I had embraced this view until faced with my own opioid addiction. Now, I realize that the world is divided between addicts who have begun to face their addictions and those who live under the illusion that they have none.
"All who have come to the point where they acknowledge their own shortcomings and realize that they cannot eliminate them through their own power have admitted that they too, in their own way, are addicts. The addiction might be to food, shopping, status symbols, the need to be 'right,' the need to be needed, or the need to feel moral superiority over those who struggle with less 'societally acceptable' sins.
"One of the most powerful teachings the church can embrace in light of this crisis is to say 'Let the one who is not an addict cast the first stone."
I found this testimonial to dovetail well with looking at Romans 7-8. Chapter 7 is depressing, as shown above: I don't do what I want to do, and I do do what I don't want to do. After that, chapter 8 is an encouragement. And in Macarthur's commentary on Romans 1-8, he says on pp. 415-16:
"In God's eyes there are only two kinds of people in the world, those who do not belong to Him and those who do. Put another way, there are only those who are according to the flesh and those who are according to the Spirit...
"Obviously there are degrees in both categories. Some unsaved people exhibit high moral behavior, and, on the other hand, many saints do not mind the things of God as obediently as they should. But every human being is completely in one spiritual state of being or the other; he either belongs to God or he does not. Just as a person cannot be partly dead and partly alive physically, neither can he be partly dead and partly alive spiritually. There is no middle ground. A person is either forgiven and in the kingdom of God or unforgiven and in the kingdom of this world. He is either a child of God or a child of Satan."
So - in other words - Christian people can struggle with addictions and still be in Christ. They aren't cast out because in this fallen world they struggle with sin issues.
And all of us struggle with some kind of sin issues. The passage also gives great hope when observing someone who has claimed Christ but is not living as he or she should.
A common bumper sticker, though trite, is still accurate: Christians aren't perfect - just forgiven. I think that the above quotations are a more in-depth explanation of that truism.