What are the ramifications of "u'Sefartem Lachem"?
Ramban: It is a Mitzvah incumbent upon every individual to verbally count the weeks and the days of the Omer. 1
Ramban: like "u'Lekachtem Lachem (in connection with taking the Arba Minim on Sukos); but as opposed to "v'Safar Lo" and v'Safrah Lah" (in 15:13, 28), in connection with a Zav and a Zavah, who are not obligated to count in order to terminate their Tum'ah (just they cannot become Tahor without counting), and "v'Safarta Lecha" (in 25:8), in connection with the Yovel, where the onus to count lies with the Beis-Din.
What are the implications of "Temimos"?
Ramban, Targum Onkelos and Targum Yonasan: It means seven complete weeks, 3 comprising the Shabbos and the seven consecutive days.
Moshav Zekenim: One begins counting at the beginning of the night, due to Temimos. Bahag says that if one missed a night, he cannot count the rest with a Brachah (for it is not Temimos). Rav Hai Gaon says that he counts with a Brachah during the day, and even if he missed an entire day, he counts with a Brachah on other days.
The question arises however - if 'Temimos' refers to the days, why does the Torah insert it together with "Shabbasos" and not with "Chamishim Yom"?
Why did the Torah command to count days until Shavu'os, unlike the other festivals?
Moshav Zekenim #1: [Before] Pesach and Sukos, people were in their houses, and when Sheluchim of Beis Din informed them of the day of Kidush ha'Chodesh, they were ready to come 1 [to the Mikdash. Before] Shavu'os they were busy harvesting, and they were not in their houses, the Sheluchim might not find them. This is why we count at night; during the day they are occupied, and are prone to forget.
Moshav Zekenim #2: Moshe told Yisrael that they will receive the Torah 50 days after Yetzi'as Mitzrayim. It was dear to them, so they counted the days. Hashem commanded this forever, to recall that dearness.
Ta'anis 10a says that it takes some people 15 days to get to the Pras river (the end of Eretz Yisrael). If so, people there could not wait for Sheluchim to come! All the more so, Shavu'os is on the sixth of the month. People more than three days journey from the Mikdash could not wait for the Sheluchim! (There are another six days of Tashlumin to bring the Korbanos, but this is b'Di'eved, and in any case people far from the Mikdash cannot wait for them. Why did Moshav Zekenim need to say that it is because people are not at home? - PF)
QUESTIONS ON RASHI
Rashi writes that mi'Mochoras ha'Shabbos" means 'the day after Yom-Tov'. If so, what does "Sheva Shabbasos" mean?
Ramban #1 (Pasuk 11) and Targum Yonasan: It means 'seven weeks'. 1
Ramban #2 (11): Both words mean 'week', and the Pasuk is saying that on the day that the Omer is waved, one begins counting the weeks of the Omer 2 - In other words, one begins counting on the day 3 after the week that has just concluded [on the first day of Yom Tov], and counts the seven ensuing weeks. 4
Ramban: As it does in Pasuk 16 (See Rashi there). The word 'Shabbos' takes on two meanings, as we find in Shoftim, 10:4 and in Melachim 2, 11:9, and the reason Chazal refer to a week as 'Shabbos' (See for example, Kesuvos, 2a) is because every week contains a Shabbos. See Ramban, who elaborates.
This explanation is based on the fact that the Torah has changed from a regular seven-day week that begins on Sunday and ends on Shabbos, to a week comprising seven days on whatever day the waving of the Omer falls, when Shabbos can fall in the middle of the week.
Ramban: the 'Mem' in "mi'Mochoras" is translated as a 'Beis', as if the Torah had written "b'Mochoras ha"Shabbos". And the same applies to "ad mi'Mochoras ha'Shabbos ha'Shevi'is" in Pasuk 16.