"For he who is least among you all--he is the greatest." (Luke 9:48)
9You, however, are controlled not by the sinful nature but by the Spirit, if the Spirit of God lives in you. And if anyone does not have the Spirit of Christ, he does not belong to Christ. 10But if Christ is in you, your body is dead because of sin, yet your spirit is alive because of righteousness. (Romans 8)
12Therefore, brothers, we have an obligation--but it is not to the sinful nature, to live according to it. 13For if you live according to the sinful nature, you will die; but if by the Spirit you put to death the misdeeds of the body, you will live, 14because those who are led by the Spirit of God are sons of God. (Romans 8)
We, who by faith have received the gift of eternal life through Christ Jesus, have also received the gift of the Holy Spirit. All who belong to Christ have the Holy Spirit within them. The Holy Spirit helps us to stop sinning among other things. If we, as followers of Christ, put to death sin in our lives with the help of the Holy Spirit we will live eternally. (Paul makes it clear that our "body is dead because of sin," yet our "spirit is alive because of righteousness." When he says that if we "put to death the misdeeds of the body," we "will live," he is talking of eternal life after our earthly death. How can Paul say that our bodies, as Christians, are dead, yet go on to say that we can live? It is obvious that he is talking about the eternal, not the mortal.)
However, there is the other side of the coin. If we live according to the sinful nature, if we follow our sinful desires, we will die. (This is talking of the second death in the lake of fire as all will die the first earthly death.)
Don't you know that when you offer yourselves to someone to obey him as slaves, you are slaves to the one whom you obey–whether you are slaves to sin, which leads to death, or to obedience, which leads to righteousness? (Romans 6:16)
We can not serve two masters. (See Matthew 6:24, Luke 16:13) You can not be a slave to both sin and obedience. It is one or the other. If you are a slave to sin, you will die. As I pointed out earlier, Paul makes it clear that we all will die here on earth, however some will die a second death while others will live. (Rev. 20:14 says, "The lake of fire is the second death.") This is clearly what Paul is referring to. Matthew 13:49-50 says, "This is how it will be at the end of the age. The angels will come and separate the wicked from the righteous and throw them into the fiery furnace, where there will be weeping and gnashing of teeth." The wicked will obviously go to hell and the righteous to eternal life.
If you are a slave to sin, you are wicked and will enter hell. If you are a slave to obedience which leads to righteousness, you will enter heaven. Again, you are either a slave to sin which will result in hell, or obedience which will result in eternal life.
When you are a slave to someone, you are obligated to do whatever he tells you to do. If the master says go work in the fields, you must go work in the fields. Likewise, if you are a slave to obedience, you must obey. There is no choice, only obligation. If you do not obey, you are a slave to sin. Sin is disobedience.
Contrary to what some Christians believe, we do have an obligation. We are obligated to live according to the Spirit. We are obligated to "put to death the misdeeds of the body." By doing this we become slaves to obedience. The result of such action is eternal life. However, if we live according to the sinful nature and are slaves to sin, we will experience the second death which is hell.