Having written - in Pasuk - "ve'Eileh Ya'amdu al ha'Kelalah", why does the Torah switch to "Arur"?
Shevu'os, 36a: To teach us thae Kelalah always incorporates 'Arur'. 1
See Torah Temimah, note 15.
What are the implications of the (otherwise superflouos) words "Ma'aseh Y'dei Charash"?
Oznayim la'Torah: It is referring to a sinner, who, in order to keep his sin secret - to avoid the death-penalty - the avoids having his image manufactured by a craftsman and makes it himself. 1
Refer to 27:15:1:1***.
What is the significance of the sins listed here? Why are they listed over and above all other sins?
Rashbam, Riva, Da'as Zekenim and Rosh: (in Pasuk 13): These are sins that people tend to perform in secret, 1 and nobody else nows about them 2 This is because sins that are transgressed openly are taken care of by Beis-Din 3 and do not require K'lalos at the Hand if Hashem. 4
Seforno: Because it was generally the leaders, over whom the people had no influence who were the perpetrators of those sins. 5
Rashbam and Riva: With the exception of Avodah Zarah and Makeh Re'eihu, which people sometimes transgress openly - and which is why the Torah adds the word "ba'Seiser".
Regarding the Arayos, the woman knows? If she consents, presumably also she is cursed; others do not know. One who hears Lashon ha'Ra, or a person disgracing his parent, he knows! Most Aveiros can be done in private, such as theft, forbidden foods, Melachah on Shabbos, wearing Sha'atnez under one's garment and Z'nus with one's daughter? (PF).
Shulchan Sh'lomoh: As opposed to sins performed in secret, whose perpetrators it is difficult to catch and punish.
Rashbam, It is in this connection that the Torah writes in Nitzavim, 29:28 "ha'Nistaros la'Hashem Elokeinu - ve'ha'Niglos lanu u'le'Vaneinu ad Olam". Oznayim la'Torah: And it is precisely because they did not accept resposibility over sins that are performed in secret, that Hashem commanded them to answer 'Amen' to the K'lalos that He placed upon those who transgress them.
Seforno: As indicated in Yechezkel, 22:6-7, where the Navi mentions most, if not all, the sins listed here, which were performed by the princes in Yerushalayim (See Seforno).
Why does the Torah insert the words "Ve'sam ba'Saser"?
Refer to 27:15:1:1*.
Avodah Zarah, 52a #1: With reference to worshipping the Avodah Zarah secretly, the Torah is teaching us here that an idol of a Yisrael does not become Asur be'Hana'ah until it has been worshipped. 1
Avodah Zarah, 52a #22. To teach us that the Avodah Zarah of a Yisrael requires Genizah. 2
Why does the Torah insert the (otherwise superfluous words "Ve'Anu Chol ha'Am Amen"?
Yerushalmi Sotah, 7:4: To teach us that not just the tribes on Har Gerizim answered 'Amen' to the B'rachos,and those on Har Eival, to the K'lalos, but both answered 'Amen' both to the B'rachos and to the K'lalos.
How can a curse suffice for someone who serves idolatry?
