Sin is transgression of the Law (1 John 3:4).
So when Paul says shall we continue in sin (i.e. Breaking of God's Laws) because we are not under the Law has got to raise a red flag for you.
Meaning, Paul is not contradicting himself here.
He cannot say that we can break God's Laws and also say that we not under no Law whatsoever.
So the only logical conclusion is Paul is talking about the Law of Moses. This makes sense because Paul was addressing the heresy of circumcision in both the book of Romans and Galatians (Do a key word search in the New Testament for the words "circumcised" and "circumcision."). For "circumcision" is a part of the Old Testament Law and not the New Testament Laws or Commands.
Also, Paul answers his question on if we can continue in sin because we are not under the Law (i.e. the Law of Moses) with:....
"God forbid."
Meaning, you cannot continue in sin.
He then says yield yourselves to whom servants you obey.
Whether it be sin unto death or obedience unto righteousness.
In other words, Paul is mentioning two contrasting kingdoms here.
1. Sin is of the devil's kingdom (1 John 3:8) and it leads to death.
2. Obedience to righteousness is of God's Kingdom and it leads to life.
Paul then also says to his brethren that they have become servants of righteousness.
Meaning, they are actually doing that which is righteous.
For John says, he that does righteousness is righteous (1 John 3:7).
Paul also says that if any man speaks contrary to the words of Jesus Christ and the doctrine of Godliness, he is proud and knows nothing.
James says God resists the proud and gives grace to the humble.
So if a beleiver is disobeying the words of Jesus Christ and says you do not have to obey His words to be saved, they are proud and they know nothing. Again, James says God resists the proud and gives grace to the humble; And logic dictates that a person cannot be saved without grace.
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