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.
And why does the Torah see fit to inform us that the seven times seven years add up to forty-nine?
Rashi #1: To teach us that, even if, for some reason, Yisrael did not keep the Shemitos, Yovel must take place after forty-nine years.
Rashi #2: To teach us that the total number of Shemitos add up to 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