וּגְּבוּל יָם וְּהָיָה לָכֶם ה יָם ה גָדוֹל וּגְּבוּל זֶה־יִּהְּיֶה לָכֶם גְּבוּל יָם: ובמדבר לד, מִּן־ה יָם ה גָדֹל תְּתָאוּ לָכֶם הֹר הָהָר: וְּזֶה־יִּהְּיֶה לָכֶם גְּבוּל צָפוֹן :ז
Gittin 8a: (Beraisa): South of the incline from Turei Amnon (to the sea) is Eretz Yisrael. North of it is Chutz La'aretz; Islands in the Mediterranean Sea within the line between Turei Amnon and Nachal Mitzrayim are part of Eretz Yisrael. Those outside this line are Chutz La'aretz.
R. Yehudah says "and the border of the sea" includes islands next to (i.e. west of) Eretz Yisrael. They are like part of Eretz Yisrael; If we extend lines westward from Kifluria and Nachal Mitzrayim (Wadi El Arish) until the Atlantic Ocean, all (islands and parts of islands) between these lines are part of Eretz Yisrael.
Question: What do Chachamim learn from "and the border of the sea"?
Answer: This includes islands within the line between Turei Amnon and the River of Mitzrayim; R. Yehudah does not require a verse to include those islands.
Understanding the Gemara
From the above verse it is evident that the mountains of Amnon (הר ההר) are rooted in the sea and they mark the northern extremity of the western border of Eretz Yisrael. The question is where in the north-west corner? (Kifluria is a town situated on the peak of the Mountains of Amnon)
The southern extremity of the western border is Nachal Mitzraim which flows into the Mediterranean Sea. According to many this is Wadi-El-Arish. But some identify it as the easternmost tributary of the Nile delta.
Although the beraisa mentions only islands, the sea itself that lies to the west are also part of Eretz Yisrael. It mentions island merely because produce, which is subject to the laws of Eretz Yisrael (such as maaser and sheviis) can apply, grow on islands.
Three times the word גבול appears in the above Pasuk. The apparently redundant term “and a border” serves to teach that Eretz Yisrael extents westward into the Mediterranean Sea. The extent of the western border is the subject of the dispute between Rabbi Yehudah and the Chachamim.
Chachamim draw a line from the northern border at Turei Amnon to Nachal Mitzrayim at the southern border. Due to the curvature of the coast, the line put the western border in the Mediterranean Sea (similar to the concept of territorial waters in international law).
Rabbi Yehudah understands the Pasuk that horizontal line is drawn from the northern and southern point extending westward. This is a large discussion of how far west. (This applies to only to islands; any continental land mass that falls between these two lines is not part of Eretz Yisrael)
Future Border
Chasam Sofer writes that the difference of opinion regarding the islands to the west of Eretz Yisrael applies nowadays. However, in the World to Come, all admit that it certainly part of Eretz Yisrael since they are included in the land of the 10 nations.
Yarden River
The eastern border of Eretz Yisrael is listed as the Yarden river, which is also a waterway. The Yerushalmi discusses if border is the west bank or east bank of the Yarden (is the river part of Eretz Yisrael or not). Either way the actual border would change each year as the river widens or narrows with the season. Perhaps, just as the western border (according to the Chachamim) is an “artificial” line of demarcation, so the eastern border might be a line (perhaps from the largest flux of the river on the east bank).
