אב מלאכה ומלאכה העושה מלאכות הרבה מעין מלאכה אחת אינו חייב אלא חטאת אחת:

and every primary category of labor that he performed. One who performs numerous prohibited labors subsumed under a single category of labor is liable to bring only one sin-offering.

גמ׳ מאי טעמא תנא כלל גדול אילימא משום דקבעי למיתני עוד כלל אחר תנא כלל גדול וגבי שביעית נמי משום דקבעי למיתני עוד כלל אחר תנא כלל גדול והא גבי מעשר דקתני כלל אחר ולא תני כלל גדול

GEMARA: The Gemara attempts to clarify the language of the mishna and asks: Why did the mishna teach the phrase: A significant principle? If you say it is because of the following reason, it is problematic.
Here, because the tanna wants to teach in a mishna later in the chapter with regard to a matter that includes two halakhot employing the term: Furthermore, they stated another principle; therefore, in this mishna, which relates to a greater number of halakhot, he taught employing the term: A significant principle.
And with regard to the Sabbatical Year as well, because in a later mishna (Shevi’it 7:2) the tanna wants to teach: Furthermore, another principle, at the beginning of the chapter he taught employing the phrase: A significant principle. There too, the choice of language is understood.
However, with regard to the halakhot of tithes, where the mishna (Ma’asrot 1:1) states two principles one after the other, the tanna taught later in the same mishna: And furthermore, they stated another principle, and even so, at the beginning of the mishna the tanna did not teach: A significant principle, opting instead to say simply: They stated a principle.

אמר רבי יוסי בר אבין שבת ושביעית דאית בהו אבות ותולדות תנא גדול מעשר דלית בה אבות ותולדות לא תנא כלל גדול ולבר קפרא דתני כלל גדול במעשר מאי אבות ומאי תולדות איכא

Rabbi Yosei bar Avin said that the term: A significant principle, is not dependent on the existence of another principle; rather, it is dependent on the significance of the principle. Therefore, with regard to the halakhot of Shabbat and the Sabbatical Year, which include primary categories and subcategories, the tanna taught in the mishna: A significant principle. With regard to the halakhot of tithes, which do not include primary categories and subcategories and all its halakhot are on equal footing, he did not teach employing the term: A significant principle. The Gemara asks: And according to the variant reading of the mishna taught by bar Kappara, who taught the phrase: A significant principle, with regard to tithes, what primary categories and subcategories are there with regard to tithes?

אלא לאו היינו טעמא גדול עונשו של שבת יותר משל שביעית דאילו שבת איתא בין בתלוש בין במחובר ואילו שביעית בתלוש ליתא במחובר איתא וגדול עונשה של שביעית יותר מן המעשר דאילו שביעית איתא בין במאכל אדם בין במאכל בהמה ואילו מעשר במאכל אדם איתא במאכל בהמה ליתא

Rather, isn’t this the reason the Mishna employs the term: A significant principle; because it is significant relative to other principles? The scope of the materials whose use warrants punishment for desecrating Shabbat is greater than the scope of the materials whose use warrants punishment for desecrating the Sabbatical Year. As the halakhot of Shabbat are in effect both with regard to plants that are detached from the ground and with regard to those that are attached, while the halakhot of the Sabbatical Year with regard to detached plants, they are not in effect, but with regard to attached plants they are in effect. And the scope of the materials whose use warrants punishment for desecrati0n of the Sabbatical Year are greater than the scope of the materials whose use warrants punishment for violating the halakhot of tithes. As, by Torah law, the halakhot of the Sabbatical Year are in effect both with regard to human food and with regard to animal food, while the halakhot of tithes are in effect with regard to human food, but with regard to animal food they are not in effect.

ולבר קפרא דתני כלל גדול במעשר גדול עונשו של מעשר יותר משל פיאה דאילו מעשר איתא בתאנה וירק ואילו פיאה ליתא בתאנה וירק דתנן כלל אמרו בפיאה כל שהוא אוכל ונשמר וגידולו מן הארץ ולקיטתו כאחת ומכניסו לקיום חייב בפיאה

And according to the opinion of bar Kappara, who taught the phrase: A significant principle, with regard to tithes as well: The scope of the materials for which one warrants punishment for violating the halakhot of tithes is greater than the scope of the materials for which one warrants punishment for violating the halakhot of pe’a. As, by rabbinic law, the obligation of tithes is in effect with regard to both figs and vegetables, while the obligation of pe’a is not in effect with regard to figs and vegetables. As we learned in a mishna in tractate Pe’a: They stated a principle with regard to pe’a: Anything that is food, and is protected, and grows from the ground, and is gathered as one, and one brings it in to storage to preserve is obligated in pe’a.

אוכל למעוטי ספיחי סטיס וקוצה ונשמר למעוטי הפקר וגידולו מן הארץ למעוטי כמיהין ופטריות ולקיטתו כאחת למעוטי תאנה ומכניסו לקיום למעוטי ירק

The Gemara explains that which is excluded by each criterion in the mishna. Food, to exclude the aftergrowths of woad [satis] and madder. As these plants are used for dyeing and not for food, the obligation of pe’a does not apply to them. And protected, to exclude ownerless crops, which by definition are not protected. And grows from the ground, to exclude truffles and mushrooms, which, unlike other plants, do not draw sustenance from the ground. And is gathered as one, to exclude the fig tree whose fruit is gathered throughout an extended period, as the figs do not all ripen together. And one brings it in to storage to preserve; to exclude vegetables, which cannot be stored for lengthy periods.

ואילו גבי מעשר תנן כלל אמרו במעשר כל שהוא אוכל ונשמר וגידולו מן הארץ חייב במעשר ואילו לקיטתו כאחת ומכניסו לקיום לא תנן:

While, with regard to tithes, we learned in a mishna: They stated a principle with regard to tithes: Anything that is food, and is protected, and grows from the ground is obligated in tithes; we did not learn with regard to tithes, the following criteria: Gathered as one, and which one brings in to storage to preserve. Apparently, figs and vegetables are obligated in tithes, making the scope of the materials obligated in tithes greater than the scope of those obligated in pe’a.

רב ושמואל דאמרי תרוייהו מתניתין בתינוק שנשבה לבין הגוים וגר שנתגייר לבין הגוים אבל הכיר ולבסוף שכח חייב על כל שבת ושבת תנן השוכח עיקר שבת לאו מכלל דהויא ליה ידיעה מעיקרא לא מאי כל השוכח עיקר שבת דהיתה שכוח ממנו עיקרה של שבת

The mishna discusses an individual who forgets the very essence of Shabbat. The Gemara seeks to understand how a Jew could forget the very existence of Shabbat. It was Rav and Shmuel who both said: Our mishna is referring to both a child who was taken captive among the gentiles and never educated and a convert who converted among the gentiles and never learned the halakhot of Shabbat. However, one who once knew of the essence of Shabbat and ultimately forgot is liable for each and every Shabbat, as we learned in the mishna with regard to one who knows the essence of Shabbat. The Gemara seeks to clarify this approach. We learned in our mishna: One who forgets the essence of Shabbat. Doesn’t this phrase indicate by inference that he was aware of Shabbat originally? In order to forget one must have previously been aware. This poses a difficulty to the opinion of Rav and Shmuel. The Gemara refutes this: No, what is the meaning of: One who forgets the essence of Shabbat? That the essence of Shabbat was always forgotten from him, i.e., he never knew it.

אבל הכיר ולבסוף שכח מאי חייב על כל שבת ושבת אדתני היודע עיקר שבת ועשה מלאכות הרבה בשבתות הרבה חייב על כל שבת ושבת ליתני הכיר ולבסוף שכח וכל שכן הא מאי היודע עיקר שבת מי שהיה יודע עיקרה של שבת ושכחה

The Gemara further asks: However, based on that understanding, in the case of one who knew the essence of Shabbat and ultimately forgot, what is the halakha? Is he liable for each and every Shabbat? If so, instead of the mishna teaching the next halakha: One who knows the essence of Shabbat and performs many labors on multiple Shabbatot is liable to bring a sin-offering for each and every Shabbat, let it teach: One who knew the essence of Shabbat and ultimately forgot and, all the more so, one who knows the essence of Shabbat would be liable for each Shabbat. The Gemara answers: According to the opinion of Rav and Shmuel, what is the meaning of the phrase: One who knows the essence of Shabbat? One who once knew the essence of Shabbat and has now forgotten it.