What are the connotations of "Keil Kana"?
Rashi: It means that, when it comes to Avodah-Zarah, Hashem is zealous - He will punish the sinner, and not pardon him.
Seforno: Hashem does not want to share His Kavod with others. 3 Consequently, when people confer Hashem's honor upon another, He is zealous for the honor that has ben conferred upon one who is unworthy of it.
Hadar Zekenim (3): Hashem loves you so much that He wants that you will be slaves only to Him, and He is angry at those who serve other gods.
As this is akin to a woman who abandons her husband and goes with another man, or to a servant who adopts another master. It does not therefore apply to other nations, whom Hashem placed under the jurisdiction of the celestial bodies (Ramban).
Since there is no one who can in any way compare with Hashem. (Seforno).
Why does Hashem wait so long before punishing the sinners?
Ramban and Seforno: He waits until their measure is full, as the generations go from bad to worse, before destroying them. 1
Like Yerav'am ben N'vat, whose children and grandchildren followed in his footsteps (Seforno). This is the explanation of the Seforno; the Ramban says virtually the same thing, adding that we never find the term "Kana" in any context other than that of Avodah-Zarah. (Bamidbar 25:11 connotes that Hashem had Kin'ah due to Zimri's Zenus, but we can say that it was due to the idolatry (25:2,3).
And to whom does "le'Son'ai" refer?
Rashi, Ramban, Rashbam and Targum Onkelos: It refers to those who go in the evil ways of their fathers.
What does "Poked Avon Avos al Banim" mean?
Ramban #1 (citing Ibn Ezra) and Targum Yonasan: It means that Hashem remembers 1 the sins of the fathers up to the fourth generation, waiting for them to do Teshuvah, and if also the fourth does not repent, He wipes them out. 2
Ramban, Seforno 3 and Targum Onkelos: Hashem avenges the sins of the father on to the sons (if they do not do Teshuvah) 4 and destroys them, and on to the grandsons or great-grandsons, 5 in the event that the measure of the previous generations are not full. 6 He does not avenge the fifth generation.
Moshav Zekenim, Hadar Zekenim (3): Normally, Hashem waits until one dies
See Ramban's interpretation of this explanation, and his objection to it).
Whereas Hashem will never punish the fifth generation for the sins of their great-great-grandfather (Ramban),
If Hashem punishes the third generation of sinners, how can there be a fourth generation?
Refer to 20:5:4:1-3.