(25:1) God spoke to Moses on Mount Sinai, saying …
God spoke to Moses on Mount Sinai, saying In this portion, the laws of shemittah—the Sabbatical Year—are outlined in great detail. Why are we told in this verse that the laws of shemittah were given at Mount Sinai? Were not all the laws given at Sinai? By associating the laws of shemittah with Mount Sinai, the Torah teaches us that just as the mitzvah of shemittah was given in the Torah with all its rules and details, so were all laws revealed on Sinai with all their rules and particulars, even though the Torah mentions them only in general terms (Torat Kohanim).
NOTE: For example, the Torah says that we should make zizith, but it does not specify how many threads and knots the zizith must contain. These details were taught in the Oral Torah, which Moses received on Sinai.
(25:11) It shall also be a Jubilee Year for you—this fiftieth year—insofar as you may not sow, harvest crops growing of their own accord, nor gather grapes from unpruned vines during that year.