a) What is “the law” according to the Apostle Paul? Explain the different usage of this word in his letters.
The Greek term for what Paul used for law is nomos. Westerholm notes that in designating nomos, the Greek term for law, it blends well in what the Hebrew word torah understand as the OT. He further explain that
“…when Paul speaks of a passage in Isaiah as coming from the “law” (1 Cor. 14:21, of Isa. 28:11-12), and provides a series of quotations from the Psalms and Isaiah (Rom. 3:10-18) as evidence of what “the law says” (v.19), his extension of the term “law” to include the sacred Scriptures as a whole can be paralled in both Greek and Hebrew sources.”
Thus on this detail we can note that “law” in its general sense of how Paul used the word incorporates the understanding that it is to the whole of the Jewish scriptures he is noting. This according to Westerholm is not disputed and many agree with this understanding.
Another way in which Paul mentions law is to designate it to something that is specific namely the Mosaic Laws. Westerholm, arguing from Romans 2 notes some peculiarity in how Paul used the word. The law, was something that Gentiles did not possess (v.14), that Jews used it to know God’s direction in how to live (vv.17-18), something that could be “done” (v.13) and “kept” (v.27). Noting this evidence, Paul in a more specific sense tell us that law “refers to the sum of specific divine requirements given to Israel through Moses.” Therefore, noting details above, when Paul mentions “the law” in a general sense of his use it points to the whole of the OT scriptures but in a more specific sense it talks about the Mosaic Law given to the Israelite community.
We can also note the different usages of the word “law” in Paul’s letters. Four can be mentioned looking to Romans where the law is seen as a controlling power (2:17-20; 9:31; 10:3-5), the Pentateuch (3:21b), the whole OT (3:19) and a principle (3:27). One might get confused if one reads Paul and interprets his use by designating the meaning of law in one meaning. As we have seen above the context and Paul’s use of the law in his arguments will determine what he means by telling his reader which designation of the law he is talking about. But one thing needs to be pointed out.
While Paul’s criticism of the Mosaic Law is not in the nature of the law but what it was unable to do in accordance with salvation, Paul tell us of another law in which Christians are to ascribe to, namely the law of Christ. Wayne G. Strickland states this as the third way in which Paul used law and this has its association to Christ. References to this law can be seen in passages such as Romans 8:2-3 and is in contrast to the Mosaic Law.
On this note, we can conclude that Paul i used ‘law’ in three different ways of understanding. On a general basis law is seen as the bulk of the Old Testament Scriptures as a whole. In further detail, Paul point to law in a specific sense where he designates it as the Mosaic Law that was given to the Israelite community at Sinai. In a third usage of law, Paul presents it as a Christian understanding where, while the control of the Mosaic law has ceased in the coming of Christ, a new law supersedes it, and that is the law of Christ.
 Westerhold, Stephen. Perspectives Old and New: The “Lutheran” Paul and his Critics. (Grand Rapids: Eerdmans, 2004). Pg 298
 Westerholm also takes note of passages in Galation 6:13 where Paul’s opponents are those who do not keep the law and more strikingly in Rom 7:7-12 where law is used interchangeably. The idea gleaned here is that Paul cauld not have wanted to point to the whole OT scriptures but to something more specific. See more in 298 -299
 Ibid. Pg 299
 Witherington, Ben.The Indelible Image: The Theological and Ethical Thought World of the New Testament. (Downers Grove: IVP, 2009). Pg 236
 Ibid 247