Why did the Rabbis forbid all sefichim (aftergrowth) of the Sabbatical year?
The Rabbis were concerned that cheaters would sow grains and vegetables discretely and then claim the produce was spontaneous sefichim. To close this loophole, they forbade all sefichim.
Question 2
Until when are sefichim of the Sabbatical year forbidden in the eighth year?
From Rosh HaShanah until Chanukah of the eighth year, sefichim of the Sabbatical year are forbidden. From Chanukah onward, the majority of produce will have grown in the eighth year, so they become permitted.
Question 3
What determines whether grain and legumes are classified as produce of the sixth or seventh year?
For grain and legumes, the determining factor is when they reach one-third of their growth (the stage at which tithes must be separated). If this occurs before Rosh HaShanah of the Sabbatical year, they are considered sixth-year produce.
Question 4
What is the positive Torah commandment described in Halachah 24?
There is a positive commandment derived from Exodus 23:11 to divest oneself from all produce grown in the Sabbatical year — leaving it ownerless so that rich and poor alike have equal access. Locking one's vineyard or fencing one's field violates this commandment.
Question 5
According to the Rambam, in which land does the Rabbinical decree forbid tilling during the Sabbatical year, so that Jews would not settle there permanently?
Although the Sabbatical year does not apply to Syria by Torah law, our Sages decreed that tilling the land there is forbidden during the Sabbatical year — specifically to discourage Jews from abandoning Eretz Yisrael and permanently relocating to Syria.