Here it says that Chizkiyah offered to pay what Sancheriv will demand, and after he sent the money, Sancheriv sent Ravshake. In Divrei ha'Yamim II, Perek 32 it says that when Sancheriv came against Arei Yehudah, Chizkiyah stopped up the springs and river, and prepared many weapons and shields, and appointed war officers, and then Sancheriv sent Ravshake!
Radak: Chizkiyah paid Sancheriv's demand annually. Later he ceased to pay, and Sancheriv returned 1 .
Malbim (Yeshayah 36:1): When Sancheriv started to conquer the walled cities of Yehudah, Chizkiyah sent for Shalom and gave the tax that Sancheriv demanded. He intended for time to prepare for war. Right after paying the tax, he strengthened the wall and brought water into the city. This aroused Sancheriv to come a second time, and he sent Ravshake. Even though he made a Bris and took a tax, he considered that Chizkiyah annulled the Bris via preparing for war.
Radak: After Sancheriv seized fortified cities of Yehudah and headed for Yerushalayim, Chizkiyah sent for Shalom and offered to pay what Sancheriv will demand. He paid, and later ceased paying. Sancheriv returned to Lachish and sent Ravshake to Chizkiyah. Chizkiyah did not accept, but Shevna made Shalom with Ravshake. Sancheriv heard that Melech Kush was coming to fight him. He went to fight Melech Kush, and threatened to return afterwards. After defeating Kush and Egypt, he returned with their spoils, and camped against Yerushalayim. An angel wiped out his camp. The survivors converted - "Ach Bach Kel" (Yeshayah 45:14). It says about them - "Yihyu Chamesh Arim b'Eretz Mitzrayim Medabros Sefas Kena'an v'Nishba'os la'Shem Tzevakos" (Yeshayah 19:18). (It seems from Divrei ha'Yamim that Radak holds that Chizkiyah prepared for war after Sancheriv returned. - PF)
Who was Ravshake?
Rashi (22): He was a Yisrael Mumar. He admits that Hashem is G-d, just [he said that] He desires [that we do] idolatry 1 . Radak - also Sanhedrin 60a says that he was a Yisrael Mumar 2 .
How can even a Mumar say so? The Torah is full of warnings against idolatry! Perhaps he said that Hashem detests serving idols themselves, but wants us to serve Him via idols (refer to 17:26:3:1). Also refer to 18:22:1:1 and the note there.
Radak: What is the source to say so? Speaking Leshon ha'Kodesh is not a proof. Many speak other languages. Elyakim, Shevna and Yo'ach knew Aramis! Perhaps Chazal had a tradition. (The Gemara inferred this, for they tore their clothes. Rav Yehudah taught that we do not tear for blasphemy of a Nochri! Perhaps Radak questions Rav Yehudah's source. - PF)
Here it says that that he sent Tartan, Rav Saris and Ravshake. In Yeshayah 36:2 it says that he sent only Ravshake!
Rashi (Yeshayah 37:36) and Radak, both citing Seder Olam 23. The first time, only Ravshake went, like it says in Yeshayah. The second time, he sent also Tartan and Rav Saris. After this, Ravshake found Sancheriv fighting Livnah (19:8)
Radak: Ravshake was primary. The others were secondary to him. We find that only Ravshake talked.
What are "Te'alah" and "Berechah"?
Rashi: They are (a) a trench, and (b) a man-made pit filled with water, to hold fish; it is long and wide.
Radak: Berechah is a pit to hold rainwater. It is made with rocks and plaster. It had a hole that was normally plugged up. The Te'alah was a pit nearby. When they wanted water to drink or for laundry, they opened the hole to fill the Te'alah from the Berechah.
Why did he send them to the Berechah?
Malbim (Yeshayah 36:2): Chizkiyah stopped up the springs and brought water into the city; he was preparing for war. This was Sancheriv's justification to fight him; the closed Berechah proved that Chizkiyah annulled the Bris.
What is "Mesilah"?
Rashi: It is a paved road.
Radak #1: It is a stone road, so one can go on it [easily, even] in winter [when earthen roads are muddy].
Radak #2: It is an expression of elevation, like "Solu la'Rochev ba'Aravos" (Tehilim 68:5). It was an elevated place in the field, fixed with stones, where people laundering in the Te'alah stood.
What is "Sede Choves"?
Rashi citing Targum Yonasan: It is a place where launderers spread out garments [Radak - to dry].
