Wouldn't it be strange and confusing to see a college student attending high school classes? Paul says, that if you are a Christian, it is just as confusing and inappropriate for you to embrace a lifestyle of sin. It goes against your new nature in Christ. To resist this back-sliding, Paul explains that we must actively present ourselves to Jesus in obedience, for Jesus is our new master, not sin.
The testimony shared on this podcast can be found here: http://daughterdisciple.blogspot.com/2014/10/half-committed.html