What are the ramifications of the words "La'asos es ha'Shabbos"?
Seforno: The Pasuk is saying that if Yisrael will keep Shabbos in this world, they will merit to keep Shabbos in the world to come.
Targum Yonasan: It means to eat delicacies on Shabbos.
Here it says "v'Shamru" before Shabbos. In Vayikra (19:3), it says "Es Shabsosai Tishmoru"!
Moshav Zekenim (16:23): This teaches that Shabbos needs Shemirah before (e.g. a tailor may not go outside carrying a needle close to Shabbos) and afterwards (do not benefit from Melachah done on Shabbos).
Mechilta d'R. Yishmael (Yisro, Masechta d'Chodesh 7 DH Zachor) learns Tosefes Shabbos before and after from 'Zachor' and 'Shamor', respectively.