Romans 3:20b, says “for by the law is the knowledge of sin.” How does this work with what the rest of the Bible says about sin? Would it really be sin to, for example, accidentally say a bad word if you didn’t know that it was one, or something of the sort? Would the sin still be yours even if you didn’t know that you were doing something wrong when you did it, or would it be on someone else because they didn’t inform you?
There are three questions here and I would like to answer them in reverse order. I will take up the general question of the relationship between the law1 and the knowledge of sin as spoken of in Romans 3:20 last. Starting with the last question first; it asks about the relationship between personal guilt and the responsibilities of others. The simple answer is that we are always responsible for what we do. This is true even in human courts of justice which are fallible. The judge may offer a reduced or even a deferred penalty, for example, if the person was not informed. In some cases, another person might be named as an accomplice or instigator. Nevertheless, we are always responsible for our own actions. The person who fails to warn us that something is wrong would be certainly failing in showing love (1 Cor 13:6).
In the second question, the issue is more specifically that of ignorance of the law. Again, even in our human jurisprudence, ignorance is not an excuse. We are required to be knowledgeable of what is lawful. In the first three chapters of Romans, the apostle shows that there are two ways mankind can know what is lawful apart from the law. In chapter 1, creation is brought forward as the witness against mankind. He writes, “For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse.” (Rom 1:20) In chapter 2 the apostle tells us that even the Gentiles can know what is lawful by their conscience which witnesses against them. (Rom 2:14, 15) So, by creation and by conscience we can know what is right and wrong. However, these are general principles. The failure of mankind during the time of Noah shows the failure of the common saying, “let your conscience be your guide.” Mankind had a conscience yet the earth was “filled with violence .” (Gen 6:13)
One final point before discussing Romans 3:20 is that we must not minimize the guilt by thinking of sin as “accidental”. The Lord in Matthew 12:36 says, “I tell you, on the day of judgment people will give account for every careless word they speak.” The point the Lord was making here is the same point the apostle is making in Romans chapters 1, 2, and 3. His conclusion is that “None is righteous, no not one.” (Rom 3:10a) In addition, the sacrifices in the Old Testament were for sins done unintentionally or in ignorance. (Lev 4:2, etc.) So, “the blood of Jesus his Son cleanses us from all sin.” (1 Jn 1:7) All this is to teach us to look away from ourselves and to the Lord Jesus in whom alone is strength for our walk with God without minimizing the seriousness of sin.
Now let’s consider the specific role of the law. A similar thought to the one given by Romans 3:20b is found in Romans 5:13 “for sin indeed was in the world before the law was given, but sin is not counted where there is no law.” Another relevant verse is Romans 7:13 where we learn that the law was given to make sin shown to be sinful beyond measure. One might be careless about the good or evil of a certain action. But, if there is an explicit commandment against some act and he does it then there is no question as to his responsibility and his being in danger of judgment. So, the law is for the purpose of putting before man very explicitly his rebellion against the righteousness of God.
There are many other things that could be said on this matter, like the fact that because sin is self-destructive the proscriptions of the law reflect the goodness of God in showing mankind how to live a life which is beneficial to both himself and others. Much suffering in society today results from simply ignoring the wisdom of the law. But, only life in Christ can give the strength for this. (Rom 8:3, 4)
1. The “law” here refers to the Mosaic law.