Salvation is Deliverance from Sin
In Romans 6:1-14, Paul evidently addresses an issue that some believers were confused by in thinking that the more they sinned, the greater the grace of God would be given. While it is true as noted in the commentary of chapter 5 that God's grace and Christ's sacrifice are sufficient to cover any and all sin that is confessed, the availability of pardon should never be used as an excuse to sin in the first place. And as it is appointed unto men once to die, but after this the judgment (Hebrews 9:27) sums up the predicament of the sinner. Everyone will die at some point, unless taken in the rapture. While it might be possible that someone would resurrect you from the dead to show the power of God, I wouldn't risk my life to prove that. For most, judgment will follow death.
Where will you be if you are willfully sinning when you die, or you die with sin that you have not confessed and sought forgiveness for? God is a righteous judge. While I do feel that His grace is perhaps larger than what we can understand, the Bible is full of warnings to not sin, and we must take them seriously. Choose to do right. Choose to abstain from evil. Accept Jesus as your Savior. That's the only certain way to reach heaven. Nobody is going to get you to heaven by a baptism after you're dead. Nobody is going to pray or bribe your way out of purgatory. There isn't any such place hinted at in the Bible. After death - the judgment. Be ready.
Our baptism into Jesus - accepting Him as Savior - was a baptism into His death as well. As Christ rose from the dead to return to the full glory of the Godhead, even so we should be raised to walk in a new fullness of life in Christ. The body of sin should have no more dominion over us and can have no more dominion over us unless we choose to let it have its way. We need to take the strength of God and choose to live for God and not allow sin to have any dominion in our body, mind, heart, soul or spirit - just to be thorough.
How do we accomplish that? Paul says in verse 12 that it is easiest to do that by yielding ourselves to God. They say idle hands are a bad thing, and I think that is manifestly true. Those who are busy have no time to sin (unless they're keeping themselves busy by sinning). Study if you are of school age. Work if you are of an age to work. Obey the prompting of the Holy Spirit to do the work that He has set out for you to do in any case. If you don't actively try to fill your day with doing God's work, you can be certain that your day will be filled with something else. Now part of the time will be perfectly innocuous. But Satan will try his best to fill any "free" time you have with sin if there is any way he can bring it about.
As you do this, by yielding your body to do good in God's sight, you make it impossible for sin to have dominion over you. Submit yourselves therefore to God. Resist the devil, and he will flee from you (James 4:7).
Our Old Relationship to Sin Compared to our New Relationship to God
In the remainder of Romans 6:15-23, Paul warns again of the dangers that sin provides to everyone, including Christians. Just because grace is easy and we aren't under the law anymore isn't an excuse to sin. Paul literally says "God forbid" us doing such a thing.
The more we choose to obey Satan's promptings and our own fleshly lusts to sin, the more we become under the dominion of that particular sin. I don't mean to deviate to try to bash some of the things that people involve themselves with that are bad for them but not necessarily sin in and of themselves, but they are good examples. One cigarette, or two or three, probably won't kill you. But the more you smoke, the more the chemicals in the cigarettes (nicotine primarily) influence your physical body until you have a craving for that nicotine that you can't escape. A person I worked with had to have major surgery and was put in an induced coma until the surgery could be performed. He said he had tried to quit smoking often, but had not been able to. But being in the coma for an extended period got all the toxins flushed from his body and when he was awakened and went through the surgery he had no more compulsion to smoke. Similar arguments can be made for drinking. Many can handle a drink or two a week. But there are others who are lost to the bottle with a single drink. It is similar to smoking. Your body can build up a tolerance to alcohol so it takes more and more to get you drunk. Soon, many find that they can't just put the bottle down anymore. They have become its servant.
But God is there to give us deliverance from sin that is complete and total - just like waking up from a coma might do. We need to become servants of righteousness at that point, doing those things that God approves of, so that we will have no time to waste doing unprofitable things of sin. That doesn't mean you can't have fun, have family time, work, go to school, or do a host of other good things that God expects you to do. But if you find you have idle time, practice turning to God to fill that time rather than listening to the wiles of Satan. He can always find something for you to do that will help to draw you away from God, little by little. As Paul points out at the end of the chapter, the end result of sinning is death.
He closes the chapter with a verse that is oft quoted as part of the Roman road to salvation: For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord (Romans 6:23). Both halves of that verse are important. If you sin, you are destined for eternal death. But God has given us a free gift of eternal life through Jesus Christ. There is no salvation through any other means. Finally, we need to make Jesus Christ our Lord as well as our Savior. We need to let Him have control over our lives 24 x 7 x 365. It is our choice to make, and nobody can make it for us. God's judgment will be sure and without appeal. Choose wisely.