Having stated "Sheva Shabsos Shanim", why does the Torah add "Sheva Shanim Sheva Pe'amim"?
Rashi: Because we would otherwise have thought that the seven Shabbos years comprise seven consecutive years.
Kol Eliyahu, Divrei Eliyahu: Had it said only Sheva Shabsos Shanim, it would suffice to count (verbally) just Shemitah years. "Tesha v'Arba'im" teaches that one must count each year. Sheva Shanim Sheva Pe'amim teaches that it is not enough to say 'this is year eight, or nine
Why does the Torah see fit to inform us that the seven times seven years add up to 49?
Rashi #1: To teach us that, even if, for some reason, Yisrael did not keep the Shemitos, Yovel must take place after 49 years.
Rashi #2: To teach us that the total number of years in the Shemitos is 49. 1
Seforno: It is a command to divide the 49 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 49 sun-years. 2
Who is commanded to count the years?