Many people nowadays believe that when it says of the Lord that he fulfilled the law [Matthew 5:17] it means that he fulfilled all of the Ten Commandments and that by doing so he became justice and justified people in the world by this act of faith.
That is not what it means, though. It means rather that he fulfilled everything that was written about him in the Law and the Prophets—that is, in the whole Sacred Scripture—because those writings, as stated under the preceding heading, are about him alone. The reason so many people believe something else is that they have not studied the Scriptures and seen what “the law” means in them.
In a strict sense “the law” does mean the Ten Commandments. In a broader sense it means everything Moses wrote in his five books; and in the broadest sense it means the whole Word.
It is common knowledge that in a strict sense “the law” does mean the Ten Commandments.
In a broader sense “the Law” means everything Moses wrote in his five books, as we can see from the following passages. In Luke,
Abraham said to the rich man in hell, “They have Moses and the prophets; let them hear them. If they do not hear Moses and the prophets, they will not be persuaded even if someone rises from the dead.” (Luke 16:29, 31)
Philip said to Nathanael, “We have found the one of whom Moses in the Law, and also the prophets, wrote.” (John 1:45)
Do not think that I have come to destroy the Law and the Prophets: I have come not to destroy but to fulfill. (Matthew 5:17, 18)
All the Prophets and the Law prophesied until John. (Matthew 11:13)
The Law and the Prophets extended to [the time of] John; since then, the Kingdom of God has been proclaimed. (Luke 16:16)
Whatever you want people to do for you, you do the same for them. This is the Law and the Prophets. (Matthew 7:12)
Jesus said, “You are to love the Lord your God with all your heart and with all your soul, and you are to love your neighbor as yourself. On these two commandments hang all the Law and the Prophets.” (Matthew 22:37, 39, 40)
In these passages “the Law and the Prophets” and “Moses and the prophets” mean everything written in the books of Moses and in the books of the prophets.
The following passages also show that “the Law” means specifically everything written by Moses. In Luke,
When the days of their purification according to the Law of Moses were completed, they brought Jesus to Jerusalem to present him to the Lord—as it is written in the Law of the Lord, “Every male who opens the womb is to be called holy to the Lord,”—and to offer a sacrifice according to what is said in the Law of the Lord, “a pair of turtledoves or two young pigeons.” And the parents brought Jesus into the Temple to do for him according to the custom of the Law. When they had completed all things according to the Law of the Lord . . . (Luke 2:22, 23, 24, 27, 39)
The Law of Moses commanded that people like this should be stoned. (John 8:5)
The Law was given through Moses. (John 1:17)
We can see from these passages that sometimes it says “the Law” and sometimes “Moses” when it is talking about whatever is written in his books. See also Matthew 8:4; Mark 10:2, 3, 4; 12:19; Luke 20:28, 37; John 3:14; 7:19, 51; 8:17; 19:7.
Then too, many things that are commanded are called the law by Moses—for example, commandments about burnt offerings (Leviticus 6:9; 7:37), sacrifices (Leviticus 6:25; 7:1–11), the meal offering (Leviticus 6:14), leprosy (Leviticus 14:2), jealousy (Numbers 5:29, 30), and Naziritehood (Numbers 6:13, 21).
In fact, Moses himself called his books the Law:
Moses wrote this Law and gave it to the priests, the sons of Levi, who carried the ark of the covenant of Jehovah, and said to them, “Take the book of this Law and put it beside the ark of the covenant of Jehovah.” (Deuteronomy 31:9, 25, 26)
It was placed beside [the ark]: within the ark were the stone tablets that are “the law” in a strict sense.
Later, the books of Moses are called “the Book of the Law”:
Hilkiah the high priest said to Shaphan the scribe, “I have found the Book of the Law in the house of Jehovah.” When the king heard the words of the Book of the Law, he tore his clothes. (2 Kings 22:8, 11; 23:24)
from The Lord, Sections 8, 9