"Sheva Shabsos Shanim" Why is the Torah effectively comparing Yovel to Sh'mitah and to years?
Yerushalmi Rosh Hashanah, 1:2: To teach us that, just like the year and Sh'mitah, 1 Yovel begins in Tishri - inasmuch as plowing and planting then become forbidden.
Refer to 25:4:0.1:1.
Why does the Torah write here "Ve'safarta l'cha" (singular), wheres in Vayikra 23:13, in connection with Serfiras ha'Omer, it wrote u'Sefartem lachem" (plural)?
Refer to 23:15:1:1*.
Having stated "Sheva Shabsos Shanim", why does the Torah need to add "Sheva Shanim Sheva Pe'amim"?
Rashi: Because we would otherwise have thought that the seven Shabbos years comprise seven consecutive years.
Kol Eliyahu and Divrei Eliyahu: Had it said only "Sheva Shabsos Shanim", it would suffice to count (verbally) just Sh'mitah years. "Tesha ve'Arba'im" teaches us that one must count each year 1 and "Sheva Shanim Sheva Pe'amim" teaches us that it is not enough to say 'This is year eight or year nine?' Rather, he must add ' ? one Sh'mitah and one year, one Sh'mitah and two years?', so that he counts seven times seven years until Sh'mitah. 2
And we learn via a Gezeirah Shavah that the same applies to Sefiras ha'Omer - Each day, one must say the total number of days, and also the weeks that have passed and how many days into the current week (Refer to 23:16:152:1 and the note there).The Torah requires this, and so is our custom, even though the Tur brings also other opinions.
Why does the Torah need to insert the (otherwise superfluous) phrase "Vehayu Y'mei Sheva Shabsos Shanim"?
Rashi #1: To teach us that, even if, for some reason, Yisrael did not keep the Sh'mitos, Yovel must take place after forty-nine years.
Rashi #2: To simply mention that the total number of years in the Sh'mitos is forty-nine. 1
Seforno: It is a command to divide the forty-nine years of the Yovel-cycle (not into years consisting of twelve lunar-months, but) by arranging leap-years when necessary, so that they correspond to the forty-nine sun-years. 2
Sifra: To teach us the obligation to verbally count the years of each Sh'mitah and from "Teshah ve'Arba'im Shanah", 3 the obligation to verbally count the years of the Yovel. 4
See Sifsei Chachamim. See also Torah Temimah (citing the Sifra).
Seforno: In the same way as one inevitably does regarding the seven-year cycle of the Sh'mitah, which is closely connected to the plowing and planting seasons. See also Oznayim la'Torah DH 'Y'mei Sheva ... '.
Much in the same way as we count the Omer. See Torah Temimah, note 40.
Who is commanded to count the years?
Rashi (on Pasuk 9) and Da'as Zekenim: It is a Mitzvah incumbent upon all individuals. 1
Hadar Zekenim: It is a Mitzvah incumbent upon the Beis Din. 2
Torah Temimah and Oznayim la'Torah: Because had the Torah wanted to obligate every indivudual to count (as it does with regard to Sefiras ha'Omer) it ought to have written 'u'Sefartem lachem' (plural), like it does there. Yovel only applies when most Jews live in Eretz Yisrael; some say that the Shevatim must also be settled in their proper locations (Refer to 25:10:4:2). That explains why we do not count Yovel nowadays (PF). Refer also to 25:8:151:1*.
