Paul explains in Rom. 3:19 that the purpose of all scripture is for Jews to conclude that no one can be declared righteous from the works of the Law. Rather, what the Law accomplishes is to define sin, and to bring its violators to where they know themselves as sinners.
“diagar vomou epignwsiV amartiaV” (for through law is full knowledge of sin“ -Rom. 3:20) With the Law, sin becomes defined as transgression and it becomes possible and therefore it is possible to have a knowledge of oneself as a sinner. Similarly, in Rom. 5:13, Paul says that where there is no law, there is no sin. Meaning that sin presupposes the Law; in the absence of the Law, there is no sin in the sense of transgression of the Law, although there may be disobedience.
The same idea is expressed in one of the most heated, and debated passages of Romans. In Rom. 7:7-8, Paul says:
“What then shall we say? Is the Law sin? Let it not be! But I did not know sin except through law; for also I did not know lust except the law said You shall not lust. But sin taking occasion through the commandment worked every lust in me; for apart fro law, sin was dead.”
“alla thn amartian ouk egnwn, ei mh dia nomou” Paul here begins to show how sins personified, used the commandment to entrap him. In his viewpoint, sin remains inactive without the Law (cf. Rom. 7:8-9) And says ironically, that with the introduction of the Law, what was intended to bring life brought death. When presented with the Law for the first time, the Hebrews naively assume that they can obey it, However, as stated before, the Law serves to nail a man to his sin, the unexpected result is that man is held in bondage to his sin so that now the Law is passively complicit in producing violations of itself. And this was the Jewish experience with the Law. As soon as he became aware of God’s requirements in the Law, their tendency to sin, defined as transgression of the Law, sprang to life. (cf. Rom. 7:9) For Paul, sin was a power that rules over, and becomes actual in the presence of the Law. Sin requires an external object in order to become actualized and the Law serves this purpose. (cf. Rom. 7:7)
This also appears the inferred meaning in Gal. 3:19a:
“Why, then the law? The transgressions because of it was added”
“ti oun o nomoV; twn parabasewn carin prosteqh” He means that the Law was added because the Jews (and indeed all mankind) are sinners. Paul uses a divine passive in this passage, so that it is God who added the Law because of transgressions. Paul does not explain in which sense the Law was added because of transgressions, but he does write: “until the seed comes to whom it was promised”. (Gal. 3:19b) This implies that one reason why the Law was added was in order to prepare for the coming of Christ, the “seed”. (cf. Gal. 3:16) Why the existence of transgressions required that the Law be made manifest is not stated. But with little doubt we can say that for Paul, the Law functioned to bring sin to light, so that they would see the need to be declared righteous apart from their own efforts or “works of the Law“. (cf. Gal.3:22-23; Rom. 3:20; 4:15; 5:13, 20; 7:7-8)[1] It is also probable that a view held by Paul is that the Law was added to define sin as sin and thereby functioned also to bring the sinner into condemnation and thusly prepare them to receive the righteousness of God.”
Many say that without the Law, as far as Gentiles are concerned, there would still be “conscious” (what Paul referred to as the “law written on the heart” [Rom. 2:15]), however, conscious does not function in the same manner as the Law because conscious can be defiled and even “seared”. (cf. 1 Cor. 8:7; 1 Tim. 4:2; Titus 1:15) Dictums of conscious are thusly liable to being rendered ineffectual, either in part, or wholly. Unlike the conscious, the Law is experienced as existing independently of the one who is subject to it, and not susceptible to perversion. The introduction of the Law has the effect of bringing into existence sin as being defined as violation of divinely -given commandment. It is also possible that Paul means that the Law was added in order to produce transgressions (cf. Rom. 5:2). This would also have the desired effect of preparing the Jew to receive the righteousness of God insofar as the more transgressions a Jew has, the less inclined they would be to deny their need of the righteousness of God.
[1] According to Hubner, Paul means in Gal. 3:19 that the Law was added in order to increase sin, so that the phrase is interpreted as a final and not a causal clause. (H. Hubner, Law in Paul’s Thought, [Edinburgh: T&T Clark, 1984], p.24-36) The Law was not added because there were transgressions, but in order to produce transgressions. In fact, Hubner argues that Paul believes it was the angels who gave the Law in order that Jews would transgress its commandments. According to Hubner, Paul later adopted a less radical view of the Law, so that the Law is now no longer understood as provoking sin, but merely as the means of knowing and recognizing sin (69-83). Under criticism by the Jerusalem church, he came to the more balanced view that the Law was on the side of God and was for that reason “holy”, “just”, and “good” (cf. Rom. 7:12) and had an important role to play in salvation history, It is probable better to say that Paul does not change his view of the Law but rather stresses the negative aspects of the Law in Galatians precisely because the Gentile believers in the Galatian churches were very close to submitting themselves to the Law as a condition of eschatological salvation. Besides, Paul does say similar things in Rom. 4:15; 5:20; 11:32 to what he says in Gal. 3:19, and Hubner’s attempts to deny this similarity is unconvincing.
From my paper: "
The Law and the Christian, A Serious Look at the Debate on Modern Day Legalism, Section 5, Various Usages of “nomoV” in the Pauline Writings, Sub-Sect. 6.1b. Rom. 3:19-20; 5:12-13; 7:7-8; Gal. 3:19"
God Bless
Till all are one.