Do you not know that to whom you present yourselves slaves to obey, you are that one's slaves whom you obey, whether of sin leading to death, or of obedience leading to righteousness? (Romans 6:16)
After stating rather firmly that Christians should not view God’s grace as a license to sin, Paul then asks a question.
“Don’t you know that you serve whoever you obey?”
In Roman society, they were all too familiar with slavery and serving a master. They knew that whoever you served was your master. How absurd it would be for someone to be set free from one master yet continue serving them!
And yet - this would be precisely what occurred if a Christian continued to “obey” and serve sin.
The Importance of Obedience.
Obedience was a central concept in Paul’s Law-free gospel, and he framed Romans with the phrase “obedience of faith” in 1:5 and 16:26. - Pollard, Truth for Today Commentary, 217
You can’t escape it - we will serve or obey somebody or something. As Christians, we have a choice.
To choose to serve Sin when Sin’s aims and goals are radically opposed to those of Christ’s is not logical. It is a repudiation of the new Master! Such a choice would be a denial of all that has been undergone and all the sacrifices made by this Master, Jesus. - McGuiggan, Romans, 196
We have been set free from sin by being immersed into the death of Jesus Christ (Romans 6:3-7). We are no longer in bondage to that master. God has set us free - and yet, He still allows us to choose who we will serve (Joshua 24:15).
The Choice is Yours.
We are not forced to be servants of sin, nor does God force us to be servants of righteousness. A man presents himself as a servant of sin or as a servant of righteousness. - Whiteside, Commentary on Romans, 138
Submitting yourself to the gospel of Christ and being immersed into the death of the Son sets you free from sin. You should then live a new life consistent with the One who has set you free.
But God allows us to choose to obey and serve Him. We also have the choice to walk back to our old master like Demas, who “loved this present world” (2 Timothy 4:10).
Which master will you serve?
You cannot serve more than one master.
No one can serve two masters; for either he will hate the one and love the other, or else he will be loyal to the one and despise the other. (Matthew 6:24)