When Paul talks about being free from sin in Romans chapter 6, he is not saying that we who are redeemed by Jesus will never sin any more. He is saying that we used to be slaves to sin, but now that we are free from sin, it no longer has control over us and we can fight it. We are now free from sin’s power.
In Anders Nygren’s comentary he says that Paul considers “free from sin” and “sinless” two different things. He is not saying that we will automatically quit sinning, but that sin no longer is our master. Jesus is now my master.
Here’s how I look at what Paul is saying: It is impossible to have sin as our master and have a little bit of Jesus. Yet it is possible, no not possible, but probable, that when we have Jesus as our master, we’re still going to have (at least) a little sin. Our hope is that little by little, as we grow in our faith and in our spiritual walk with Jesus, that more and more He helps us say no to sin. So that there is continuously, “More of Him and less of me” in our lives. And that’s what United Methodists mean when we say we’re “going on to perfection”.