So, what is the obligation of which Paul speaks? The first hint is in the latter part of verse 13, ..."but if by the Spirit you put to death the misdeeds of the body, you will live,..." That's certainly true, but it still does not tell us what the obligation is.
Then Paul seems to abandon the subject and goes off in different directions. Some seem to think he was spacey and disjointed. Nothing could be further from the truth.
From Romans 8:14 through Romans 11:36 Paul is setting the stage for the obligation. He says that since the Holy Spirit testifies about Jesus, since Jesus willingly died to save us and sent His Holy Spirit to encourage us, since we who know Jesus are more than conquerors, and so on, we have an obligation and he reveals that in chapter 12:1 - "...present your bodies as living sacrifices."
Paul actually states specifically what our obligation is, but he wants us to know why we have the obligation. That's the reason for the parenthetical explanation in between the "...we have an obligation..." and the statement of the obligation: to "present your bodies as living sacrifices..." The sentence, without the parentheses, reads like this: We have an obligation to present ourselves as living sacrifices...
That is why reading Scripture as a narrative, instead of little pieces here and there, is so important. If we do not read it as a narrative, we stand the chance of drawing many different conclusions, many of which are not even related to the point.
Often the chapter and verse divisions of the Bible (which are not part of God's inspiration) hinder us from understanding the point. Without the point, the Scripture might very well be improperly applied.
God did not design the Bible for proof-texting. No part of the Scripture stands alone. It all has to be understood in terms of the word used, the verse it's in, the chapter it is in, the book the chapter is in, the covenant to which it applies and to the Bible as a whole. Anything else cheats the meaning of any passage.
Learn to read the Bible as a narrative rather than a series of proverbial thought. Then it always demonstrates continuity. It makes sense!
