Why did he say "Nakel la'Tzitz Eliezer Lintos"?
Rashi: It is easy for the shade to stay in its place. To go back, after it was afternoon to return to be morning, is astounding.
Radak (9): The sun goes quickly. It is easy for it to go faster than normal. Going backwards is a greater sign.
Ralbag: The sun did not go back, just the shade did 1 . The clouds reflect sparks of light from the sun. Chizkiyah understood from the clouds and vapors that it is not such a wonder if the shade will advance, only if it will go back. The Mofes was not elsewhere; Melech Bavel sent Sheluchim "Lidrosh Es ha'Mofes" (Divrei ha'Yamim II, 32:31), i.e. that Chizkiyah recovered 2 .
Malbim (Yeshayah 38:8): It is not such a wonder for the shade to lengthen by itself. If the sun will go back, this is a great wonder!
Malbim (Divrei ha'Yamim II, 32:24): In Sefer Melachim, it is called an Os. Here Ezra calls it a Mofes, to teach that it was a proper miracle; the sun's course was altered.
This is like Pirkei d'R. Eliezer 52 and Bereishis Rabah 65:9, that before Chizkiyah, no one became ill and recovered. (PF)