Rashi comments on (3:1) וְאֵלֶּה תּוֹלְדֹת אַהֲרֹן וּמֹשֶׁה בְּיוֹם דִּבֶּר ה׳ אֶת מֹשֶׁה בְּהַר סִינָי that even though the pasuk is speaking about Aharon's children, they are called Moshe's תּוֹלְדֹת because לפי שלימדן תורה, מלמד שכל המלמד את בן חברו תורה, מעלה עליו הכתוב כאילו ילדו. Netziv explains at length that לימדן תורה in this context means specifically חכמת התלמוד. Moshe taught Torah to all of Klal Yisrael, but they are not called his תּוֹלְדֹת because he did not (at least at this point in time) give over to them that added level of pilpul that he shared only with the Bnei Aharon. Netziv then asks on himself: the pasuk is talking about what took place בְּהַר סִינָי, at the moment of kabbalas haTorah. At that moment, Moshe was not being mi'palpel with the Bnei Aharon. At that moment Moshe was not sharing חכמת התלמוד with the Bnei Aharon. Why then already at that moment are they called Moshe's תּוֹלְדֹת?
Netziv answers that even though on that day the Bnei Aharon had not yet started learning from Moshe, nonetheless באותו יום קבלו עליהם ללמוד ממנו אח״כ, on that day they made a kabbalah and accepted upon themselves to become his students. Therefore, it was from that moment that their status changed.
Netziv proves his point from the story (BM 84) of Reish Lakish, who started out as a bandit/robber. One day he jumped into the river to chase after R' Yochanan, but R' Yochanan turned the tables on him and was able to convince Reish Lakish to take his great strength and dedicate his kochos to learning Torah. The gemara then says that Reish Lakish found himself unable to jump out of the river he had just jumped in to. Rashi explains: ולא מצי. לקפוץ כבראשונה דמשקבל עליו עול תורה תשש כוחו Reish Lakish hadn't learned a single daf yet or spent a single day in the beis medrash, but once he was mekabel upon himself to learn Torah, he became a changed person.
This is what Chag haShavuos is all about. Even if you stay up both nights of Shavuos and manage to not sleep a wink in the day as well, you are not going to finish shas or Shulchan Aruch in 2 days. But the point of the holiday is not to have a cram session. The point is to make a kabbalah. It's not how much you cover during those 48 hours that will make a difference, but rather what you are mekabeil upon yourself in those 48 hours to accomplish during the next days, months, years ahead that will make the difference.
We celebrate 6 Sivan and not just 7 Sivan, which was the actual date of kabbalas haTorah. Moshe added an extra day so Hashem gave us the Torah on the seventh, but we still celebrate on the 6th because that is the day when we were already ready to receive it, when our kabbalah to accept it was made. That is as worthy of celebration as the actual giving on the Torah b'poel that took place on the next day.
The Midrash on the pasuk in Rus (2:12) יְשַׁלֵּם ה׳ פׇּעֳלֵךְ וּתְהִי מַשְׂכֻּרְתֵּךְ שְׁלֵמָה מֵעִם ה׳ אֱלֹקי יִשְׂרָאֵל אֲשֶׁר בָּאת לַחֲסוֹת תַּחַת כְּנָפָיו comments אָמַר רַבִּי חָסָא אֲשֶׁר בָּאת לַחֲסוֹת תַּחַת כְּנָפָיו. All the sifrei dersush ask what R' Chasa adds to what the pasuk already tells us. The Sanz Klausenberger (5733) explains that the Midrash is coming to justify Boaz's promise to Rus of מַשְׂכֻּרְתֵּךְ שְׁלֵמָה, a complete reward. Even though in point of fact Rus had not yet done anything yet as a Jew to earn reward, she deserved it anyway because she took upon herself a kabbalah. The decision to make a commitment and throw one's lot in with Klal Yisrael, אֲשֶׁר בָּאת לַחֲסוֹת תַּחַת כְּנָפָיו, irrespective of what might happen going forward, is itself a life changing act. Shem m'Shmuel similarly writes that we have a principle that mitzvah goreres mitzvah. Good deeds create their own inertia, their own snowball of positive energy that keeps going. Reward is not given for following that path of inertia, but rather for the initial kabbalah that set things in motion.
This also explains R' Yosef's cryptic remark that, "If not for this day [of Shavuos], there are many other Yosef's in the marketplace." R' Yosef forgot his learning due to illness. He went from being Rosh Yeshiva to knowing no more than any other Joe on the street. If all that mattered was what you know -- how many sugyos, how many blatt -- then Rav Yosef was washed up. But it's not just what you know that counts, but what you aspire to know, the kabbalah to try and know. Rav Yosef could not remember his learning, but he still had the desire to remember, the desire to learn, the kabbalah to do better if he could.
I've written before that I am not a big fan of staying up all night on Shavuos and then the next day of Y"T or next Shabbos going right back to davening at 9:15. (I think last time I wrote I said 9:00, but now shuls have pushed the starting times even later.) Doing that is a one night stand. Mattan Torah is "yom chasunaso." When you get married, hopefully it is a lifelong commitment, not a one night celebration. It's a kabbalah about how you intend to live your life going forward. That's what we should be striving for.