‘Or are you ignorant, brothers (for I speak to men who know the law), that the law has dominion over a man for so long time as he lives?'
The ‘or', and the argument, both look back to Romans 6:14, ‘you are not under the Law but under grace'. In dealing with this Paul expresses his confidence that the Roman Christians were not ignorant of what the Law taught. This would be true, 1) because many of them were Jewish Christians; 2) because even more had probably been God-fearers before they became Christians, attending the synagogue and listening to the reading of the Law without actually becoming Jews by circumcision; 3) because the remainder, while being Gentile Christians, would have become aware of the teaching of the Law due to the fact that the Old Testament Scriptures were the Scriptures of the early church, and would be studied as such. Thus they all ‘knew the Law'. And the emphasis that he is bringing out is that, outside of Christ, the Law has dominion over a man while he lives. It seeks to control every aspect of his life. Thus the man is bound by the Law until he dies. Deliverance from the Law can only come about through death. And he is about to demonstrate that that is precisely what has happened.
We should note that the Law that he is mainly talking about is the Law as it was known to the Jews through the teaching of the Rabbis, a Law that was laid out in a series of demands and which commanded obedience to even its minutiae. To come short of that Law in any way was to be rendered ‘a sinner', and that meant to the Jews being in danger of not enjoying eternal life and having to start again on the endless road of Law-keeping. It was a Law which put men under a burden that they could not bear (Acts 15:10; Philippians 3:6 with Romans 7:7-10). Life became an endless attempt to observe the Law, an attempt which eventually had to fail, and meanwhile kept the mind from such ideas as mercy, compassion and justice (Matthew 23:23). It was a Law from which Christ came to set us free. Paul probably also had in mind that many of the Christians in Rome were subject to Judaising tendencies (Romans 14:2-6; Romans 14:15; Romans 14:20), although he does not attack them for that, presumably because they did not put them forward as ‘necessary for salvation'. What he is against is the Law presented as essential for salvation.
It could be argued that for Gentiles ‘the law' in question was the law written in their hearts as they revealed a sense of right and wrong (Romans 2:14), but that the main emphasis is on the Jewish Law comes out in the illustration that follows.