I have found consistently when the subject of submission to human authority comes up people will object on the basis of the imperfection of human authority. It seems a part of human nature to find excuses not to submit to authority. We may demonize them in our thinking, only calling to mind their sinfulness so as to feel justfied in rebelling against them. I'm sure that Paul often was faced with Christians complaining about the injustice and oppression of the Roman authorities. Of course human authority only has a limited realm of authority, but within that realm they are legitimate God-ministering authorities. And in this sense Paul is speaking of these civil authorities. If they are rewarding evil and punishing good, they are acting outside their legitimate realm of authority. But that does not nullify their God-given authority to reward good and punish evil. The Old Testament has many examples of God using pagan authority figures as his ministers, and punishing them if they overstep their authority. “亚述是我怒气的棍，手中拿我恼恨的杖。” 以赛亚书１０：５
At the time, FEAR was the primary motivator to get people to submit to authority. The more rebellious the people, the more oppressive the Romans were. The Romans even developed crucifixion to terrorize the people into submission. However, Paul was introducing another motivation here - submission FOR CONSCIENCE SAKE. As imperfect as they were, these civil authorities were legitimate ministers of God. I suppose that Paul empathized with them, as he also was a minister of God in a position of authority. And he also motivated people to follow Jesus out of fear and for conscience sake.
(vs 6) Taxes
And just as he had argued in 歌林多前书９ that ministers have a legitimate right to get payed for ministering (though he himself had chosen not to), so also he views taxes as a sort of tithe to God. In Moses' time, both social and religious programs were supported by tithes and offerings. Much of our taxes provide for social security - for the elderly and other social programs for the poor. They go to paying government authorities and programs much as the Mosaic tithe went to paying the Levites and the Temple. So when you pay your taxes, you are fulfilling a religious duty.
(vs 7-8a) Debts
There are legitimate monetary debts that we have, as well as being in debted to respect and honor those in authority. These Paul views as responsibilities we are obligated to fulfill. He is not preaching freedom from debt as freedom from responsibility. But rather freedom from debt, having fulfilled our responsibilities. "Owe no one anything" does not mean that you should take out loans, but rather the idea is "fulfill the obligations that you have to others". So with respect to loans, pay your loans on time according to your agreement.
It is interesting the Paul mentions respect and honor. Money is usually most on people's mind when they think of debt. I'm sure there were Christians thinking, "Isn't it enough that we have to pay these secular civil authorities. But now we also have to respect and honor them as well!"
(vs 8b-10) Love
Here's a debt that we should never really think that we've completely fulfilled. We shouldn't think - "I loved my neighbor yesterday. That's all he's going to get from me!" Love for others goes beyond just a responsibility. It should be a part of who we are and what we do. And if we love, we are already fulfilling our social responsibilities as summarized in the 10 commandments. One way to measure your love for others is to ask youself or your neighbor, "What harm am I doing to my neighbor? And what good?" (Directly or indirectly) Love demands discerment, for without it, you may not realize what harm or good you are doing to others. (腓立比书１：９－１１)
(vs 11-14) Enlightened Behavior
The salvation Paul is referring to is the completion of our salvation with the return of Christ and the redemption of our physical bodies. With this is view, we should behave appropriately, just as the Apostle John also says in 约翰一书３：２，３. In which case, a Christian's behavior is really a measure of his faith.
"Decently" is not that measured by the world, but by Biblical standards, controlling the passions of the flesh.
The "armor of light" (vs 12) is mention in 以弗所书６：１１－１８, and is also related to the statement "clothe yourselves with the Lord Jesus Christ" (vs 14). Having established the motivation for decent behavior, Paul gives the model of decent behavior - the Lord Jesus Christ. The gospels then become central to the Christian life, as they describe Christ and his behavior.
Though our flesh craves to sin, yet we should ignore such cravings and rather focus on Christ - honorable and appropriate behavior, fulfilling our responsibilities, in view of the fruitfulness it will produce and the glory at Christ's return.