Why will Hashem give a sign? Achaz did not want one!
Rashi: He will give to you against your will [Radak - in order that you will believe in Him, against your will!
Who is the girl?
Rashi: It is my (Yeshayah's) wife. She will become pregnant this year, the fourth year of Achaz' reign 1 .
Radak: Almah is not a Besulah, rather, a youth 2 , like a Na'arah, whether Besulah or Be'ulah - "Derech Gever b'Almah" (Mishlei 30:19) refers to a Be'ulah. She was the Navi's wife or Achaz' wife. The latter is correct; if she were Yeshayah's wife, it would have said ha'Nevi'ah, like it says below "va'Ekrav El ha'Nevi'ah" (below, 8:3). Also, "Melo Rochav Artzecha Imanu'el" (8:8) implies that it was the king's son.
Rashi: Some say that the baby was Chizkiyah. This cannot be, for he was born nine years before his father's reign [began]! Radak (15) - also, his mother was not Almah (young) when this Nevu'ah was said..
Radak: Similarly, a young male is called Elem - "Ben Mi Zeh ha'Elem" (Shmuel I, 17:56).
Is she already pregnant?
Rashi: No. "Harah" is future, like we find regarding Mano'ach's wife. The angel told her "v'Harisa? Hinach Harah" (Shoftim 13:3, 5).
Malbim: Yes.
How will she know to call the baby "Imanu'el"?
Rashi: Ru'ach ha'Kodesh will rest on her.
Malbim: Here Hashem commanded her 1 to do so.
Why didn't Hashem command him? Radak - Perhaps based on custom, it was upon her to choose the name. (PF) Hadar Zekenim (Bereishis 38:4) - it was customary for the father to name the first son, and the mother, the second.
Why will she [as opposed to the father] name the baby?
Radak: It was customary for the mother to name the children.
What is the significance of the name "Imanu'el"?
Rashi: Our Rock (Kel) will be Imanu (with us).
What is the sign [that the Nevu'ah will be fulfilled]?
Rashi #1: She was a Na'arah, and never had Nevu'ah, and for this, Ru'ach ha'Kodesh will rest on her 1 . This is why it says below "va'Ekrav El ha'Nevi'ah" (8:3). We do not find that a Navi's wife is called a Nevi'ah, unless she herself had prophecy!
Rashi #2: She was young, and not proper to give birth.
Radak: Now she is pregnant; now she will give birth, and she will call his name Imanu'el 2 .
Malbim: There was no wonder or miracle in this sign. It is a mere Siman, like "u'Kshartam l'Os Al Yadecha" (Devarim 6:8). The command to call him Imanu'el is a sign that Hashem is with us. Also the other Simanim that he gave, e.g. calling the [other] son "Maher Shalal Chash Baz" (8:3), and writing the scroll (8:1) were mere signs. Meforshim toiled in vain to find miracles in them. If a Navi says from the beginning what will happen in the end, this is a sign that his Nevu'ah is Emes. Sometimes a Nevu'ah for bad is not fulfilled, if the Rasha repents, like Yirmeyah told Chananyah ben Azor (Yirmeyah 28:9) 3 . When Hashem commands to do an action with the Nevu'ah, it will be fulfilled in every case. Therefore, the command to call the babies 4 Imanu'el and Maher Shalal, and to write in the scroll, was a sign that He will not retract even if the nation changes 5 .
What is the Siman? Perhaps Yeshayah or someone who heard this prophecy will tell her! Radak (Shmuel I, 19:24) says that when Nevu'ah comes on a person, his senses are Batel and he falls, like it says about Bil'am "Nofel u'Geluy Einayim" (Bamidbar 24:4) and Daniel "Hayisi Nirdam Al Panai u'Fanai Artzah" (Daniel 10:9). Sometimes he removes his clothes. Perhaps it was recognized that she had prophecy at the time she gave the name. (PF)
If she will give birth now, obviously now she is pregnant! If she was not pregnant before, and she will immediately become pregnant and give birth, this is an awesome miracle, far greater than calling him Imanu'el! Perhaps everyone discussed the miraculous birth, and via this everyone heard the name and its significance. Also the name was a Siman, if Achaz ensured that no one tell her the prophecy. (PF)
There, it says that if a Navi prophesizes Shalom, and it is fulfilled, it is known that he is a true Navi. (PF)
Malbim (8:1): He commanded to call the second baby "Maher Shalal Chash Baz."
"Imanu'el" is a sign that He will be with us. Maher Shalal hints to the fall of Retzin and Pekach; this is good for Yehudah, and bad for the 10 tribes. Both will occur, even if the nation repents or becomes worse. (PF)
