One mitzvah, or many?
ויקהל משה את-כל-עדת בני ישראל ויאמר אלהם אלה הדברים אשר-צוה יקוק לעשת אתם: ששת ימים תעשה מלאכה וביום השביעי יהיה לכם קדש שבת וגו’ ויאמר משה אל-כל-עדת בני-ישראל לאמר זה הדבר אשר-צוה יקוק לאמר: קחו מאתכם תרומה ליקוק כל נדיב לבו יביאה את תרומת יקוק וגו’
Moshe gathered the entire assembly of the Children of Israel. He said to them: “These are the matters which Hashem commanded to do: Six days you shall work, and on the seventh day it shall be for you a Holy Shabbos”…Moshe said to the entire assembly of the Children of Israel, saying: “This is the matter that Hashem commanded, saying: Take for yourselves a donation for Hashem. All those with a generous heart will bring their portion for Hashem”
This week’s parsha begins by speaking about the mitzvah of Shabbos. It then continues with a detailed description of the construction and materials of the Mishkan, the portable Temple the Jews built in the wilderness. There’s a discrepancy with how these two mitzvos are introduced. The mitzvah of Shabbos is described as, “these are the matters which Hashem commanded”, and the mitzvah of constructing the Mishkan is described as, “this is the matter”. Besides the inconsistency, these descriptions are also counterintuitive. One would think that Shabbos is only one prohibition, to refrain from creative labor. This is unlike the construction of the Mishkan, which involves many parts, such as the Ark, the Altar, the Menorah. Why then is Shabbos described in the plural, and the Mishkan in the singular?
In terms of counting mitzvos, the Rambam teaches us that we should count only one mitzvah to build the Temple. Although there are various stages of the construction of the Mishkan or Holy Temple, including the Temple vessels and the gathering of their materials, those are all simply preparatory actions. They aren’t mitzvos in and of themselves. Only the mitzvah itself, to construct the Temple, should be counted. This could be the intent of the verse, which describes the construction of the Mishkan as, “this is the matter”. The Torah views all the stages of construction as simply a means to one end, building the Temple.
Now, it’s true that Shabbos is only one prohibition against creative labor. However, our Sages tell us that someone who brazenly transgresses Shabbos in public is as if they had violated the entire Torah. The converse is that anyone who observes Shabbos properly is as if they had fulfilled the entire Torah. Therefore, this is clearly alluded to when the Torah refers to Shabbos as “these are the matters”, in the plural. Shabbos is very much relevant to many, in fact all the mitzvos. Furthermore, to demonstrate that this only true if someone brazenly transgresses Shabbos in public, and not in private, the Torah gave Shabbos this description adjacent to the words, “Moshe gathered the entire assembly”. Only then would it be considered as if they had violated the entire Torah. Good Shabbos
 Based on Chasam Sofer Al HaTorah to Exodus 35:1
 Exodus 35:1,2,4,5
 Sefer HaMitzvos Shoresh § 12. See also § 10
 Ibid Aseh § 20
 ככופר בכל התורה כולה. Perhaps his source is Midrash Aggadah to Numbers 15:36. See also Zohar II parshas Yisro p. 90a, which says ומאן דמשקר בשתב משקר באורייתא כלא. See as well Yerushalmi Nedarim 3:9
 Zohar Chadash Bereishis Midrash Ne’elam p. 17a (this is how I found it cited in a few places, but I personally found it on p. 29b). The Chasam Sofer quotes these two statements from Chazal like it’s one source, but I couldn’t find an early source which combined them together. Many later sources quote it like this as well, including Chofetz Chaim Al HaTorah Ma’amarim Ma’amar Zichru Toras Moshe