Why does the verse attribute the lineage of Achaz, who was a Rasha, to his righteous fathers?
Rashi (from Bereishis Rabah 63:1): The verse ends "[Melech Aram] could not fight against it." This shows that [even though Achaz was a Rasha], the merit of his fathers stood for him. The angels said, who is this evil king [for whom You give special protection]? Hashem said, he is the son of Yosam and the [grand]son of Uziyah. His fathers were Tzadikim, therefore I cannot [let others] attack him.
Why does it say "Alah" and "Lo Yachol" (singular)? Retzin and Pekach came to fight!
Radak: Retzin was primary. He brought Pekach with him.
Malbim: Initially, Retzin came by himself, and Pekach came by himself (Divrei ha'Yamim II, 28:5-6). Each of them conquered Yehudah, but neither could combat Yerushalayim by himself.
Why was he unable to fight against it?
Refer to 7:1:1:1.
Radak: It was not due to the strength of Yehudah and Yerushalayim. They feared lest he capture Yerushalayim! Rather, Hashem did not want to hand Yerushalayim over to the enemy, for merit stood for it. Also in the days of Chizkiyah, [Hashem saved it] "Lema'ani u'Lema'an David Avdi" (37:35).
