G‑d commands Moses regarding the Sh'mitah (Sabbatical) and Jubilee years. Every seventh year is a Sabbatical year, when it is forbidden to work the land (in the Land of Israel). After seven sets of seven years a Jubilee year is proclaimed by a blast of the shofar (ram's horn) on that year's Yom Kippur. During Jubilee years all the laws of the Sabbatical year apply, and, in addition to the Sabbatical laws, all slaves are set free and all lands revert to their original owners.