Ki Tavo: Adoption In Public of Required Behavior in Private

That seems to be the theme in parshat Ki Tavo, in perek 27. They stand in public on Har Gerizim and Har Eval and in between, and accept certain private practices on penalty of a curse. Thus,

יא וַיְצַו מֹשֶׁה אֶת-הָעָם, בַּיּוֹם הַהוּא לֵאמֹר.	11 And Moses charged the people the same day, saying:
יב אֵלֶּה יַעַמְדוּ לְבָרֵךְ אֶת-הָעָם, עַל-הַר גְּרִזִים, בְּעָבְרְכֶם, אֶת-הַיַּרְדֵּן: שִׁמְעוֹן וְלֵוִי וִיהוּדָה, וְיִשָּׂשכָר וְיוֹסֵף וּבִנְיָמִן.	12 'These shall stand upon mount Gerizim to bless the people, when ye are passed over the Jordan: Simeon, and Levi, and Judah, and Issachar, and Joseph, and Benjamin;
יג וְאֵלֶּה יַעַמְדוּ עַל-הַקְּלָלָה, בְּהַר עֵיבָל: רְאוּבֵן גָּד וְאָשֵׁר, וּזְבוּלֻן דָּן וְנַפְתָּלִי.	13 and these shall stand upon mount Ebal for the curse: Reuben, Gad, and Asher, and Zebulun, Dan, and Naphtali.
יד וְעָנוּ הַלְוִיִּם, וְאָמְרוּ אֶל-כָּל-אִישׁ יִשְׂרָאֵל--קוֹל רָם. {ס}	14 And the Levites shall speak, and say unto all the men of Israel with a loud voice: {S}
טו אָרוּר הָאִישׁ אֲשֶׁר יַעֲשֶׂה פֶסֶל וּמַסֵּכָה תּוֹעֲבַת יְהוָה, מַעֲשֵׂה יְדֵי חָרָשׁ--וְשָׂם בַּסָּתֶר; וְעָנוּ כָל-הָעָם וְאָמְרוּ, אָמֵן. {ס}	15 Cursed be the man that maketh a graven or molten image, an abomination unto the LORD, the work of the hands of the craftsman, and setteth it up in secret. And all the people shall answer and say: Amen. {S}
טז אָרוּר, מַקְלֶה אָבִיו וְאִמּוֹ; וְאָמַר כָּל-הָעָם, אָמֵן. {ס}	16 Cursed be he that dishonoureth his father or his mother. And all the people shall say: Amen. {S}
יז אָרוּר, מַסִּיג גְּבוּל רֵעֵהוּ; וְאָמַר כָּל-הָעָם, אָמֵן. {ס}	17 Cursed be he that removeth his neighbour's landmark. And all the people shall say: Amen. {S}
יח אָרוּר, מַשְׁגֶּה עִוֵּר בַּדָּרֶךְ; וְאָמַר כָּל-הָעָם, אָמֵן. {ס}	18 Cursed be he that maketh the blind to go astray in the way. And all the people shall say: Amen. {S}
יט אָרוּר, מַטֶּה מִשְׁפַּט גֵּר-יָתוֹם--וְאַלְמָנָה; וְאָמַר כָּל-הָעָם, אָמֵן.	19 Cursed be he that perverteth the justice due to the stranger, fatherless, and widow. And all the people shall say: Amen.
כ אָרוּר, שֹׁכֵב עִם-אֵשֶׁת אָבִיו--כִּי גִלָּה, כְּנַף אָבִיו; וְאָמַר כָּל-הָעָם, אָמֵן. {ס}	20 Cursed be he that lieth with his father's wife; because he hath uncovered his father's skirt. And all the people shall say: Amen. {S}
כא אָרוּר, שֹׁכֵב עִם-כָּל-בְּהֵמָה; וְאָמַר כָּל-הָעָם, אָמֵן. {ס}	21 Cursed be he that lieth with any manner of beast. And all the people shall say: Amen. {S}
כב אָרוּר, שֹׁכֵב עִם-אֲחֹתוֹ--בַּת-אָבִיו, אוֹ בַת-אִמּוֹ; וְאָמַר כָּל-הָעָם, אָמֵן. {ס}	22 Cursed be he that lieth with his sister, the daughter of his father, or the daughter of his mother. And all the people shall say: Amen. {S}
כג אָרוּר, שֹׁכֵב עִם-חֹתַנְתּוֹ; וְאָמַר כָּל-הָעָם, אָמֵן. {ס}	23 Cursed be he that lieth with his mother-in-law. And all the people shall say: Amen. {S}
כד אָרוּר, מַכֵּה רֵעֵהוּ בַּסָּתֶר; וְאָמַר כָּל-הָעָם, אָמֵן. {ס}	24 Cursed be he that smiteth his neighbour in secret. And all the people shall say: Amen. {S}
כה אָרוּר לֹקֵחַ שֹׁחַד, לְהַכּוֹת נֶפֶשׁ דָּם נָקִי; וְאָמַר כָּל-הָעָם, אָמֵן. {ס}	25 Cursed be he that taketh a bribe to slay an innocent person. And all the people shall say: Amen. {S}
כו אָרוּר, אֲשֶׁר לֹא-יָקִים אֶת-דִּבְרֵי הַתּוֹרָה-הַזֹּאת--לַעֲשׂוֹת אוֹתָם; וְאָמַר כָּל-הָעָם, אָמֵן. {פ}	26 Cursed be he that confirmeth not the words of this law to do them. And all the people shall say: Amen.' {P}

Let us go through each one of these one by one. They said each of these in a loud voice, as it states וְאָמְרוּ אֶל-כָּל-אִישׁ יִשְׂרָאֵל--קוֹל רָם.

1. The graven or molten image, which he "setteth it up in secret."
2. Dishonoring father or mother is private behavior. Sometimes it emerges into the public sphere, as in the case of ben sorer umoreh, but usually this is personal, family behavior.
3. Removing the neighbors landmark is something which would kind of have to be done in secret, because it is hidden theft and claiming that his land now belongs to you.
   
4. Misleading the blind probably will not come back to haunt you, since he will be unlikely to identify you.
5. Perverting the justice due to the stranger, fatherless, and widow, is rendering a judgment and pretending that this is the valid judgment for them.
6. Incest and bestiality are things usually done in private.
7. Cursed be he that smiteth his neighbour in secret -- once again, we have the stress on secrecy, and thus on private behavior.
8. Taking a bribe to slay an innocent person, also seems secretive.
   

All of these must be confirmed in public to perform them, though the actual performance is in private. This might be obvious, but it is still good to make it overt.