What is the connection between the Korban Omer and Sefiras ha'Omer on Pesach and the Sh'tei ha'Lechem on Shavu'os?
Ramban: One begins to count the Omer at the beginning of the barley harvest, on the day that one brings the first produce of the barley crops together with a Korban; whereas the Sh'tei ha'Lechem comprises the first produce of wheat, which is also brought together with a Korban. 1
Ramban: Which is secondary to the Minchah regarding both the Omer and the Sh'tei ha'Lechem.
Until when does one count the Omer?
Rashi: One counts the Omer up to the end of the seven-week period 1 - 49 days.
Rashi: Because the word "Ad" (in the phrase "Ad mi'Mochoras ha'Shabbos ha'Shevi'is" is exclusive.
What are the connotations of "Minchah Chadashah"?
Rashi: It is the first Korban that is brought from the new wheat crops. 1
Ramban: It is a prohibition against bringing a Minchah from the new crops before the Sh'tei ha'Lechem.
Rashi: Even though the Omer preceded it, the Omer was different, inasmuch as it consisted of barley, whereas all other Menachos (with the sole exception of the Minchas Kena'os of a Sotah) consisted of wheat.
How do the words "Chamishim Yo"m fit into the Pasuk?
Rashi #1: "Chamishim Yom" goes together with the following phrase 1 , to read "Chamishim Yom v'Hikravtem Minchah Chadashah la'Hashem".
Rashi #2: One needs to invert "Tisperu" and "Chamishim Yom", in which case "Chamishim Yom" goes together with "Mochoras ha'Shabbos ha'Shevi'is, with which it is synonymous.
Hadar Zekenim: It means 49, for it says "Shiv'ah Shavu'os" (Devarim 16:9) This is like "Arba'im Yakenu", which means 39.
Rosh: A support is the Ta'am (note) Tircha on the word "Tisperu", which shows that it refers to what came before, and not to "Chamishim Yom." (There is an Asnachta under Yom. This shows that Chamishim Yom is not read with v'Hikravtem! - PF)
Why are the Sh'tei ha'Lechem called "Minchah Chadashah"?
Rashi and Rashbam: Because it is the first Korban that is brought in the Beis-Hamikdash from the new produce. 1
Seforno (on Pasuk 17): The Omer is brought from the first produce of barley, and the Sh'tei ha'Lechem, from the first produce of wheat. 2
Why does a Zav or Zavah not count with a Brachah? He (or she) is similarly commanded "v'Safar Lo" or "v'Safrah Lah"!
Rosh, Moshav Zekenim: A Zav or Zavah cannot count with a Brachah, lest he or she see (Zivah or blood, which cancels the count).
Why does it say "Shiv'ah Shavu'os Tispar Lecha" (Devarim 16:9), and "Tisperu Chamishim Yom"?
Moshav Zekenim: This teaches that it is a Mitzvah to count days and also weeks. 1
We hold like R. Yosi, that the Torah was given on the seventh of Sivan. How do we say on the first day of Shavu'os 'Zman Matan Toraseinu'?
Hadar Zekenim: Since there is only one day until Matan Torah, this is not a problem.
Ha'Kesav veha'Kabalah: The Torah did not make Shavu'os dependent on Matan Torah, rather, on Sefiras ha'Omer. Chak Yakov (494:1) - this is like Rivash (96), that we are not concerned if Shavu'os falls on the fifth of Sivan (when they were Mekadesh the month via witnesses), even though all agree that Matan Torah was on the sixth or seventh. 1
Magen Avraham (Reish 494, citing Asarah Ma'amaros): This is a hint to Yom Tov Sheni of Galus 2 (the second day of Shavu'os).
How is this like Rivash? He taught that we are not concerned for the day of the month, only for the 50th day from the Omer. Here, we ask why we say 'Zman Matan Toraseinu' on the wrong day of the Omer! (PF)
Chak Yakov (494:1): Why is the day of Matan Torah Yom Tov Sheni? And this does not help for Bnei Yisrael, who observe only one day!
Why don't we bless on counting years until Yovel? There is a similar command "u'Sefarta Lecha" (25:8)!
Moshav Zekenim: Only Beis Din is commanded to count years until Yovel. Perhaps they blessed!