There is a concept that there are 613 biblical commands. However, a careful examination reveals that there is no biblical teaching that there are 613 commands, and there are far less than 613 biblical commands.
Rabbi Simlai’s Sermon
The first report that the Torah contains 613 commandments occurred in the third century CE, when Rabbi Simlai mentioned it in a sermon that is recorded in the Babylonian Talmud, Makkot 23b. It appears that he invented the number 613 because it made his point: A person should observe the Torah with all his body parts (248) every day (365), the two numbers equaling 613. The Talmud states: “Rabbi Simlai gave as a sermon (darash Rabi Simlai): 613 commandments were communicated to Moses, 365 negative commands, corresponding to the number of solar days [in a year], and 248 positive commands, corresponding to the number of the members [bones covered with flesh] of a man’s body.”
As far as we know, no one had a concept that there were 613 biblical commandments before Rabbi Simlai offered his sermon. In fact, 150 years before Rabbi Simlai, Ben Azzai is quoted as saying there are 300 biblical commands. E. E. Urbach wrote: “in the Tannaitic sources this number  is unknown.”
The Reaction of Abraham ibn Ezra, Nachmanides, and Others
Ibn Ezra (1089-1167) recognized that if one counts all of the divine commandments recorded in the Bible, the number would be well over a thousand; and that if only the commandments relevant to his day were numbered, the total would be less than three hundred. He wrote in his Yesod Moreh 2, “Some sages enumerate 613 mitzvot [divine commandments] in diverse ways…but the truth is that there is no end of the number of mitzvot…and if we were to count only the root principles…the number of mitzvot would not reach 613.”
Nachmanides (1194-1270) writes in his Hasagot, his critical commentary to Maimonides’ Sefer Hamitzvot, that the 613 count is a matter of dispute and there is no certainty that it is true, but since “this total has proliferated throughout the aggadic literature…we ought to say that it is a tradition from Moses at Sinai.”
Judah ibn Balaam (eleventh century) rejected the notion that there are 613 biblical commands. He wrote “To my mind, the dictum [of Rabbi Simlai] was said only as an approximation.”
Gersonides (1288-1344) also rejected the idea that there are 613 biblical commandments. He wrote that the number is only homiletical, teaching that Jews should obey God’s laws with their entire being (248 organs) every day (about 365 days in the solar calendar.
Rabbi Shimon ben Tzemach Duran (1361–1444) summed up the above-mentioned views: “Perhaps the agreement that the number 613…is just Rabbi Simlai’s opinion, following his own explication [account] of the mitzvot. And we need not rely on his explication when we come to determine the law, but rather on the Talmudic discussion.”
Enumerating the Biblical Laws
In view of the facts mentioned above, it should come as no surprise that the enumeration of 613 biblical commandments was first mentioned to dramatize a sermon and the early attempts to list the 613 commandments failed because there are not 613 biblical commands. In his introduction to his own listing, in Sefer Hamitzvot, Maimonides (1138-1204) pointed out some attempts to list the 613, including such errors as inserting post-biblical rabbinical commandments such as the lighting of Chanukah candles in the list of biblical commandments.
Maimonides’ itemization of the 613 biblical commandments is the most logical, but it is not accepted by all rabbis. Nachmanides, for example, rejected some of his items and included others.
There is one serious problem with Maimonides’ list of biblical commands. Most of the laws in Maimonides’ list, if not all of them, have been modified and explained by the rabbis in ways that are not explicit in the Torah. For example, Rashbam (c. 1085- c. 1158) recognized that when the Bible states that the law that is being mentioned shall be a sign between the eyes and a sign on the hand it means that the law should be remembered always whenever you look or do anything. He was explaining that the law of tephilin, which the rabbis derive from these verses, is not the original biblical intent.
Yet Maimonides includes tephilin as two of the 613 biblical commandments, listing a commandment that was apparently enacted by the rabbis and, in any event, not explicitly written in the Torah as biblical.
How Should Maimonides Be Interpreted?
It would be absurd to say that Maimonides did not realize that virtually all, if not all, of the commandments that he enumerated are the rabbinical interpretation of the Bible, not explicit biblical commandments. Thus, although he does not say so, we should understand that he listed those commandments that the rabbis said were biblical in origin because while they are not explicit in the Torah, the rabbis classified them as biblical because they used biblical words as pegs (called asmachta) for their laws.
In short, a careful examination of Maimonides’ Sefer Hamitzvot, which contains his listing of the 613 commands and his Mishneh Torah, his Code of Jewish laws, shows that the rabbis changed Judaism. They gave the Hebrew Bible a meaning that is not the literal meaning of the text, changed the biblical laws, and invented laws which were later included in the list of 613 biblical commands.
How many of the commands are relevant today?
Not only is the number 613 the result of a third century sermon, with the list debated by many rabbis, and includes commands instituted by the rabbis who considered them “as if” they were biblical, most of the inventory of 613 commands are not relevant today.
In his Sefer Hamitzvot, Maimonides enumerated the positive commandments which “a Jew in the ordinary course of life has always the opportunity to fulfil.” Maimonides records only 60 commands, not 248, that are applicable to men. The number for women is only 46. Chavel states that one could add 23 other commands to the list, commands that were added by Rabbi Israel M. Kagin (called the Chafetz Chaim – 1839-1933). These are laws that most Jews rarely if even need to observe, such as redeeming the firstling of an ass, cancelling claims in the Sabbatical year, the extinction of Amalek, and unloading a tired animal. Even if these 23 are added to Maimonides’ 60 for men and 46 for women, the total of 83 and 69 fall far short of the 248 traditional number of positive commandments.
 Sifrei Devarim 76.
 The Sages, Their Concepts and Beliefs, Cambridge, 1997.
 By “diverse ways,” ibn Ezra meant that rabbis differed in many ways what they included in the 613 “biblical commandments.” Bachya ibn Pakuda (eleventh century), for example, considered that only practical duties and not beliefs should be included in the 613 commandments, although Maimonides included beliefs, so he had a different list of 613 commands (in Hovot Halevavot [Duties of the Heart], Feldheim, 1984).The most famous catalogue is that of Maimonides, discussed below, but as we will see, Maimonides included in his list of “biblical commandments” laws that are not explicit in the Torah but which the rabbis instituted using Torah wording as a peg upon which they attached their law.
 Nachmanides’ willingness to call a doubtful idea “a tradition from Moses at Sinai” is remarkable. It is clear that what he means by the term is not, as many think, that these laws were literally obtained by Moses from God at Sinai, but since the notion of 613 commandments has become part of Jewish tradition, we should consider the idea important as if they were revealed at Sinai.
 Harkavy, Abraham E., “Zikhron ha-Gaon Shmuel ben Hofni u-Sefarav,” Zikaron leRishonim ve-gam le-Aharonim, vol. 2 (St. Petersburg: 1880), pp. 41-42. Also cited by Perla in his introduction to Sefer Ha-Mitzvot L’Rasag.
 See M. Kellner, Torah in the Observatory, Academic studies Press, 2010.
 in Zohar Harakia, Academic Studies Press, 2012.
 One example is whether there is a biblical command to dwell in Israel; Maimonides did not list it, while Nachmanides included it in his catalogue.
 Exodus 13:9, 13:16; Deuteronomy 6:8–9 and 11:18.
 The rabbis use two terms medioraita, “from the Torah,” and miderabbanan, “from the rabbis,” to classify the origin of laws. These terms should not be taken literally. A law is often called mideoraita even though it is clearly not mentioned in the Torah, because the rabbis found an asmmakhta, a pin or nail upon which they could hang their decree.
Albert D. Friedberg also noted that Maimonides included rabbinic laws in his itemization of 613 commandments in Crafting the 613 Commandments: Maimonides on the Enumeration, Classification, and Formulation of the Scriptural Commandments, Academic Studies Press, 2014. Friedberg writes: “the heavily politicized atmosphere of Cairo, where Rabbanites were both assiduously courted and continuously attacked by sectarian groups (largely Karaites) over the role of the oral law in interpreting Scripture, Maimonides chose to keep his radical opinions hidden yet recoverable. When applied to the legal sections of the Torah, Maimonides’ peshateh di-qera hermeneutics [interpreting scripture according to its plain meaning in context rather than the manner that rabbis used to teach their laws] would likely raise hackles among his own co-religionists and, worse yet, give comfort to the deniers of the oral law. His carefully planted literary clues could lead the reader who is familiar with rabbinic terminology and unburdened by popular and superficial conclusions to discover the Master’s true opinion or at the very least sense his ambivalence.”
 One way of seeing this is to look at what Maimonides states is a biblical command and then look at the verse that he sites to show where the Torah mentions the command. In many instances, this examination will reveal that the quoted text does not explicitly mandate the command. A further examination will reveal that even if the Bible text does contain the command, the details of its implementation are not in the Torah, but were developed by the rabbis. Examples of commands that are not really in the Bible include: a mandate to believe in God, cleaving to God, reading the shema, studying the Torah, the two command regarding Tefillin, the mezuzah, grace after meals, shechitah, counting the omer, fasting on Yom Kippur, resting on Yom Kippur, reading the prophets, abiding by a majority decision, and more.
 Maimonides The Commandments, translated by Charles B. Chavel, The Soncino Press, 1967, pages 348-349.
 The quote is from Chavel.
 In Sefer Ha-Mitzvoth Hakotzer, published by Rabbi David Katz, 2000.
 Maimonides did not itemize the negative commands that are relevant today, probably because strictly speaking, all of the prohibitions are in effect today, even though in many instances people would not have an opportunity to do the act today. Rabbi Israel M. Kagin listed 200, again far short of the traditional number 365. The total, according to Rabbi Kagin’s register is 283, less than half the 613 number.