Romans 8:12 says, "So then, brethren, we are under obligation, not to the flesh..."
This is the second time Paul has used the word "obligation" in Romans. He used it in his opening statement to the church in 1:14 when he said "I am under obligation both to Greeks and to barbarians, both to the wise and the foolish." 7 chapters later and we hear it again.
The context of chapter 8 is an exciting one. In the first 11 verses Paul seems to be responding to his statement in 7:23 which talks about the war that is in the life of the believer.
In the first 4 verses he reiterates what he spoke following 3:24--when the Roman citizen (who I see as the person Paul is speaking to throughout Romans) is saved--up to Chapter 8. He simply reminds that Jesus has fulfilled the Law. And this freedom now reigns in the citizen. And then in v.5-8 he challenges the citizen to surrender and submit to God. And then in v.9-11 it all comes together by citing that because of our saved position and our submission we are able then to combat that war of our body that is spoken of in 7:23.
Throughout these verses it is the Holy Spirit and our submission to Him which yields a completely changed person. And when we submit and surrender we change to such a degree that He "gives life to your mortal body." The body that has been at war within ourself, between the law of my mind and the members of my body (7:23) can now be given life. Wow. How amazing this is when we simply submit and surrender. Easier said than done.
So, we now move to verse 12 and realize that "we are under obligation, not to the flesh." The surrender and submission is not an option when we arise each day. The KJV uses the word "debt to the flesh."
Debt is a pretty easy word to understand these days. And now we must think of our submission and surrender to Him in the same way. It is imperative. Think of what happens to life if we skip the mortgage payment on the house, so therefore every effort is made not to let this happen. We must then submit to our Father in the same way, with the same level of urgency; with the same sort of obligation.
I admit I don't think of my time with God each day with that type of requirement. Often, I look at it more as an option. Or a choice. I guess it is a choice, but how many of us would choose to lose our house?