For whom is this sign?
Rashi: It is for Chizkiyah, to know that you will have food. Rashi (Melachim II, 19:29) - even after Sancheriv fell, they feared starving to death.
What is the sign?
Rashi, from Targum Yonasan: When you see Sancheriv return to his land and fall, you will know that the second promise [about what you will eat] will be fulfilled.
Rashi (Melachim II, 19:29): When you see the hordes (Sancheriv's army) fall, that is a sign that also the promise of food will be fulfilled.
Radak (Melachim II, 19:29): The first Nevu'ah was that Sancheriv will hear [about Melech Kush] and return to his land. You know that it was fulfilled from Sancheriv's second message to you. Also the Nevu'ah "Bazah Lecha
Rashi in Melachim writes that even after Sancheriv fell, they feared starving to death. What is the reason?
Rashi: Sancheriv destroyed the land and cut the trees. 1
Radak (Melachim II, 19:29): They had not seeded the land that year, due to Sancheriv's army.
Radak (Melachim II, 19:29, citing Seder Olam 23): Sancheriv came two weeks before Pesach, so they could not seed 2 .
There should have been plenty of food from the spoils of Sancheriv's army, like after Aram fled from Shomron (Melachim II, 7:18)! Surely there were less than 1,000,000 people in Yerushalayim. Shevna had 130,000 followers, and they would have been the majority, if Resha'im were included in the count (Sanhedrin 26a)! Rashi explained that Ashur had at least 370,000,000 soldiers (refer to 36:9:1:1). If they destroyed the land, surely they had rations to eat during the siege. Each Jew could survive on the rations of 370 soldiers for a long time! Perhaps the rations were perishable, and would not last until the land could produce. (PF)
They could seed only after his camp died, on Pesach, so the grain was permitted only after offering the Omer a year later. Therefore, the Navi tells what they will eat, b'Heter. This does not explain why there was mortal danger. Piku'ach Nefesh overrides Chadash and other Isurim! Normally, people sow at the beginning of winter (Bava Metzi'a 106b). Perhaps this year they did not, for they expected Ashur's army to return, just like Chizkiyah closed the springs. However, this does not show that he was adamant that they not find food in the land. Armies normally take food for themselves, but not water! (PF)
What will they eat in the coming years?
Rashi: The second year, fruits will grow from the cut trees.
Radak (Melachim II, 19:29): They knew that the first year they will eat Sefichim (what grows by itself), for they had not seeded. The Chidush was this it will be blessed, and it will suffice for them. The second year, they will eat Shachis (what grew from what fell from the Sefichim). The third year, they will plant what was left over from the Sachish, and reap without fear of enemies.
Why does it say here "Shachis", and in Melachim II, 19:29, "Sachish"?
Radak: These are the same, just the letters are re-arranged, like Kesev and Keves, Salmah and Simlah.
