Concise Bible Dictionary:
The subject of “law” is not restricted in scripture to the law given by Moses. God gave a commandment (or law) to Adam, which made Adam’s subsequent sin to be transgression. Where there is no law there is no transgression (Rom. 4:15), though there may be sin, as there was from Adam to Moses: “until the law sin was in the world, but sin is not imputed [or put to account] when there is no law” (Rom. 5:13). This doubtless signifies that specific acts were not put to account as a question of God’s governmental dealings, when there was no law forbidding them. Men sinned, and death reigned, though they “had not sinned after the similitude of Adam’s transgression” (Rom. 5:14), for no definite law had been given to them. The nations that had not the law were however a law unto themselves, having some sense of good and evil, and their conscience bore witness accordingly. It is not a true definition of sin, to say that it is “the transgression of the law,” as in the AV of 1 John 3:4. The passage should read “Sin is lawlessness:” that is, man doing his own will, defiant of restraint, and regardless of his Creator and of his neighbor.
“Law” may be considered as a principle in contrast to “grace,” in which sense it occurs in the New Testament, the word “law” being often without the article (though the law of Moses may at times be alluded to in the same way). In this sense it raises the question of what man is for God, and hence involves works. “The doers of [the] law shall be justified” (Rom. 2:13); but if, on the other hand, salvation be “by grace, then is it no more of works: otherwise grace is no more grace” (Rom. 11:6). The conclusion is that “by the deeds of [the] law there shall no flesh be justified in his sight.” None can be saved on that principle. In opposition to it “the righteousness of God without [the] law is manifested.” The believer is “justified freely by his grace through the redemption that is in Christ Jesus” (Rom. 3:20-24). “Law” as a principle stands also in scripture in contrast to “faith.” “The just shall live by faith: and the law is not of faith; but the man that doeth them shall live in them” (Gal. 3:11).
The word “law” is also used for a fixed and unvarying principle, such as “a law of nature”; thus we read of the “law of faith,” “law of sin,” “law of righteousness,” “law of the Spirit of life,” (compare Rom. 7:21).
The term “law” is occasionally used in the New Testament as a designation of other parts of the Old Testament besides the Pentateuch. The Lord said, “Is it not written in your law, I said, Ye are gods?” when the quotation was from the Psalm. John 10:34: similarly 1 Corinthians 14:21.
The LAW OF LIBERTY, (James 1:25; James 2:12), implies that, the nature being congruous, the things enjoined, instead of being a burden, are a pleasure. Doing the commandments of the Lord is the fruit of the divine nature: they are therefore both law and liberty.