The interesting thing about Orthodox Judaism is that it is very, very old, and at the same time, relatively new.
Now of course, that statement is going to need some explanation.
What we refer to as Orthodox Judaism has been practiced for thousands of years. However, this does not mean that it is practiced today the same way as it was practiced several thousand years ago. Far from it! Over the years the Rabbis have added many different practices, along with many restrictions, that have all had a major impact on Orthodox Jewish life today.
But this is all part of the system that was originally instituted. The Torah was given to the Jews with the understanding that the Rabbis would have the right to add certain elements when they saw a need to do so. The process through which this takes place is complex and beyond the purview of this article.
What do we mean when we say that Orthodox Judaism is new? For thousands of years there was only one thing called Judaism and so, there was no need to describe any form of Judaism as “Orthodox”. It was only during the period of the enlightenment that there arose a movement to “reform” Judaism and give it a new form. The primary motivation to do so was to help the Jews be more acceptable to the nations amongst which they lived.
Once there was a Reform Judaism (and later Conservative Judaism), those who still believed that Judaism was still the same old religion it had been all along began to be referred to as Orthodox Jews.
There is a point here that is very important to clarify. When we say that until the enlightenment there was only one form of Judaism, that is not to say that until that time Judaism was monolithic. There have always been many debates between Jewish scholars on everything from theological matters, to questions of how to understand statements in the Torah, to questions of Jewish law. Some of these debates even grew very heated. The important thing is that the debates take place within a certain framework. They were based on an acceptance of the premise that the Torah was given on Mt. Sinai and we are bound to follow it. The Torah doesn’t change with the times; it is eternal. Once we have accepted that, we can debate endlessly (that’s what Jews do!) what the Torah meant, and how to apply it to new situations. The important thing is that everyone is agreeing to the “rules of the game;” the rule being that if we can prove that this what the Torah says, this is what we have to believe and do.
The Reformers changed all that. They said that the Torah has to be change and adapt to the modern world. The people who rejected that premise and said we have to be faithful to the original understanding of Torah and Judaism, became known as Orthodox Jews.