In 1 John 3:4, sin is defined as transgression of the law of God. Can you please tell me which law is being referenced? Thanks. -- Cyndi H.
In 1 John the term law refers to God's will for everybody -- whereas in Romans and Galatians it refers to the Torah (the law of Moses). Which makes this a great question. Unfortunately, many commentators fail to understand Paul, for whom the question of whether Christians must observe Torah was a huge question. Hebrews, Colossians, and Ephesians explore the relationship between the old law and the new covenant. (See also Acts 15.) Many writers are also unduly influenced by Luther, who tended to equate law with works and works-righteousness. This identification flowed from his own spiritual experience -- yet this is not what Romans is dealing with.
A good illustration of law in the broader, non-Mosaic-Law, sense is Matt 7:23, where we read, "And then will I declare to them, 'I never knew you; depart from me, you workers of lawlessness.'" Jesus has just said that those who don't do the will of the Father in heaven are in for a shock (7:21).
For help with any NT verse, see the NT Chapter Studies (nearly 400 pages of material covering all 260 NT chapters).