What are the connotations of "Eish Ochlah Hu"?
Ramban: With reference to the fire that Yisrael saw on Har Sinai, it refers to the Midas ha'Din that avenges the sin of Avodah Zarah.
Seforno: 'Eish Ochlah Eish', implying that the Fire of Hashem will consume the Soul together with the body.
What exactly, does "Keil Kana" mean?
Rashi: It means that Hashem is zealous - that He is angry and punishes those who worship Avodah Zarah.
Seforno: With reference to those who worship Avodah Zarah, it is because there is no existence that can compare to that of Hashem, and that consequently, someone who worships any other god, is ascribing to it what belongs to Hashem alone, and is akin to a woman who gives to another man what is designated for her husband exclusively.
How can Hashem have Kin'ah (envy)? A Chacham envies only another Chacham. A Gibor (powerful one) envies only another Gibor!
Avodah Zarah 55a: A parable for this is a man married to Leah. He then married a second wife. If the latter more distinguished than Leah, Leah does not resent him for this. If she is less distinguished 1 , Leah resents him for this.
Rosh (32:17): Hashem is doubly angry because you yourselves know that idols are futile. (He brings this parable, but distinguishes between whether or not the latter is more beautiful.)