Romans 6:[12] Let not sin therefore reign in your mortal body, that ye should obey it in the lusts thereof. [13] Neither yield ye your members as instruments of unrighteousness unto sin: but yield yourselves unto God, as those that are alive from the dead, and your members as instruments of righteousness unto God. [14] For sin shall not have dominion over you: for ye are not under the law, but under grace. [15] What then? shall we sin, because we are not under the law, but under grace? God forbid. [16] Know ye not, that to whome ye yield yourselves servants to obey, his servants ye are to whom ye obey; whether of sin unto death, or of obedience unto righteousness?
In other words, you may be saved; but, if you are serving Sin, you are dealing to yourself, death. As my mother used to say, "buy 'em books and buy 'em books and all they do is look at the pictures". If one cannot sin or if one's sin cannot hurt them, such a warning is not necessary. And there is no mistake here as in chapter 8 that he is talking to saved Christians. Getting saved is the first step. Being obedient in our walk is the rest of the road. If you get saved then serve the devil, you're out of your mind if you think you're going to heaven - having served the devil all your days after being saved. The Bible speaks to that too - And guess what, it doesn't say they were never saved in the first place, it says once saved and turned away.