Here are some raw figures to contemplate about the usage of “law” (Greek: nomos) in the NT (relying on Bibleworks):
- Total NT occurrences: 199x (including references to “the Law and the Prophets”
- Of these, total occurrences in the entire Pauline Corpus: 95x
- Of these, 82x occur in Romans (56x) and Galatians (26x). In 1 Corinthians 6x, Philippians 3x, 1 Timothy 3x, Ephesians 1x.
- The other significant numbers are Acts 18x, John 13x, and Hebrews 13x, 10x in Luke
- Cf. 8x in Matthew (wouldn’t you expect more?)
Clearly, the sizeable numbers of usages are in writings that address questions about Jesus-faith and the OT and/or concerns about Torah-observance and its role now in the new setting occasioned by Jesus’ death and resurrection.
To focus on Paul, the term appears with frequency only in two writings: Romans and Galatians, and only 9 other times scattered across 1 Corinthians and Philippians among the uncontested letters of Paul. No uses at all in 2 Corinthians, 1 Thessalonians, Philemon, or in 2 Thessalonians, Colossians, 2 Timothy, Titus.
I get the impression that Paul engaged “the Law” when required to do so in the course of his mission to bring former pagans to faith in Jesus and commitment to the God of the Bible. So, e.g., the densest usage in Galatians was obviously provoked by those who seem to have been promoting Torah-conversion among Galatian churches to complete their conversion to God. And the largest single number of uses in Romans, likewise seems to have been prompted by Paul’s need to set out his mission and teaching with the aim of securing the acceptance of Roman churches, and to correct any misrepresentations of him there, especially by Jewish believers who opposed or suspected the terms of his gentile mission.