Whereas an eternal law has no end, a finite law does. There are many commands in Torah that Hashem has given, which are meant only for a particular period of time.
For example, when G-d told Abraham to slay Isaac, that was a unique command. It was not given to all of G-d’s people, and it is not a standing order for fathers to slay their sons. Another instance of a finite command was when Moses made the fiery serpent and set it on the standard, and whoever looked at it would live. That was not something that regularly happened in the days of Moses and throughout the history of Israel – it was a unique command never to be duplicated.
And so now we have discussed the two categories of law, in regards to duration. All laws are either eternal or finite. There is no third option. A law, once it is given, either lasts forever, or it ceases at a certain point in time.
When we speak of a particular law being eternal, we are not saying that it is without beginning and without end. Only Hashem is without beginning – everything else has an origin. And so an eternal law is one that starts at a particular point in time, and then carries on forever. Once it is instituted, it is always required to be obeyed.
Examples of eternal laws can be found in the ten commandments found in Exodus 20:
You shall not murder. You shall not commit adultery.
G-d never approves of murder or adultery. It doesn’t matter the culture, it doesn’t matter the era. It doesn’t matter if it is a Jew or a Gentile, it doesn’t matter if it was 1000 years ago or is 1000 years from now. Such heinous acts are never permissible and always sinful in G-d’s eyes.
So when we hear the rabbis speak about the eternal Law of Moses, we need to realize what they are teaching is that each and every individual law that makes up the whole body of law is eternal in duration. If all of the single laws are not eternal in duration, how then can the entire collection of laws be eternal in duration, since the whole is simply the sum of the parts?
What is the Torah?
The answer depends on the context.
Torah can simply mean instruction. Or it can refer to the five books of Moses. Or it can refer to the 613 commandments derived from the five books of Moses.
When rabbis speak of the Torah, they often mean the 613 commandments of Moses. And when they are asked if Abraham obeyed the Torah, they answer “Yes”. But they do not distinguish between the Law of Moses and the Torah that Abraham followed. This is troubling, because we know they were different, if not by a lot, then by a little.
How do we know this?
Abraham did not tithe to the Levites, as required by Moses
Abraham did not observe the Passover, as required by Moses.
Abraham did not observe Yom Kippur, as required by Moses.
Since Abraham predated both the tribe of Levi and the exodus from Egypt, he could not follow commands that had no meaning in his day.
Listen below to Rabbi Tovia Singer explaining how Abraham obeyed the Torah. This is an example of how Orthodox teaching adds to Tanakh, for Tanakh knows nothing of Abraham obeying the Law of Moses.