In the conclusion of his Introduction, the Rambam explains why he undertook to produce the Mishneh Torah, and how he structured his magnum opus.
Summary: The Rambam explains that following the completion of the Talmud, persecutions of the Jewish people increased and the exile got progressively worse. At the same time, the Sanhedrin was disbanded years earlier, and there was no longer a recognized body of Sages that could rule on Jewish matters by majority vote. Individual rabbis in distinct communities around the world would make rulings based on their own understanding and for the needs of their particular communities. Such rulings cannot be applied to all of the Jewish people worldwide! The Rambam makes clear that the only laws that can be said to be binding upon all the Jewish people are those set forth in the Talmud, based strictly on the Mishnah and Tanakh. Meanwhile, the language of the Talmud (Aramaic) was no longer understood by the majority of Jews now spread around the world. Thus, the Rambam undertook to codify the entire Talmud, and put it into simple Hebrew language that all could understand. This would be a unified, singular text that would make clear exactly which laws a Jew must follow, “so that a person will not need another text at all with regard to any Jewish law.” The Rambam explains that he called his code the Mishneh Torah, literally meaning a “repetition” or “second” to the Torah, because “a person should first study the Written Law, and then study this text and comprehend the entire Oral Law from it, without having to study any other text between the two.” A Jew need only read the Torah of Moses itself, along with the Mishneh Torah of Moses Maimonides, to grasp the entirety of Jewish law! Finally, the Rambam concludes by stating that, as is well-known, there are 613 commandments in the Torah, and he has structured his code of law around those mitzvot. Under the general heading of each mitzvah, he will explain all the halakhot that fit under it, as we shall see.
Insight: Although the Rambam called his text the Mishneh Torah, it came to be better known as the Yad HaChazakah, “the Strong Hand”. One reason for this is to avoid confusion with the fifth book of the Torah, Devarim, which was historically referred to as Mishneh Torah as well because it repeats and reviews much of what happened in the Torah previously. (This is also why it is known in English as Deuteronomy, meaning “repetition”.) Secondly, it is to avoid confusion with the Mishnah, the first corpus of Jewish law that was composed by Rabbi Yehuda haNasi. Finally, the word yad (יד) in Yad HaChazakah has a numerical value (gematria) of 14, alluding to the 14 volumes within the Mishneh Torah. It is also interesting to note that yad means “hand”, and the human hand has five fingers which are composed of 14 phalanges or segments (two in the thumb, and three in each of the other fingers). The term Yad HaChazakah comes from the Torah’s description of how God redeemed us and took us out of Egypt with a “Strong Hand”. Our Sages taught (Sanhedrin 98a) that when all of the Jewish people properly adhere to God’s Law, the Final Redemption would come immediately. It is therefore most appropriate to refer to the Mishneh Torah as the Yad HaChazakah, for through its observance we will merit to once again be redeemed by God’s Strong Hand.
For an inside look at the Mishneh Torah’s introduction and a further insight, see the following short video: