Rashi, Ramban #1 (citing Sanhedrin, 43b), Rashbam, Seforno ¹ and Targum Yonasan: Refer to 29:28:1.1:1. ²

Ramban #2: It teaches us that Hashem will take care of sins of which the perpetrator himself is unaware (the Shegagos) and not punish him, ³ and it is only for sins of which he is aware (which he perpetrates be'Meizid) that we are all held responsible.

Seforno: Even though Moshe said earlier that they were all standing before Hashem who would punish them if they broke the covenant - since nobody can fool Him, that was only as far as the hidden sins is concerned, but when it comes to the sins that people know about, the onus lies on us to punish the evildoers.

Rashi (citing R. Nechemyah in Sanhedrin, 43b), Rashbam, Seforno, and Ramban: Hashem punishes the Tzibur only for known sins of others, if they do not eradicate the evil from their midst, but not for sins that others perform in secret. ¹

Rashi (like R. Nechemyah in Sanhedrin 43b): To teach us that even for known transgressions, ¹ the Tzibur will be held responsible only after they cross the Yarden and accept the oath on Har Gerizim and Har Eival. ²

Da'as Zekenim #1, Hadar Zekenim #1 and Rosh: Really, there should be dots on "la'Hashem Elokeinu", since it is from them that we exclude hidden transgressions, but it is inappropriate to place dots on Hashem's name, since it looks as if it has been erased. And seeing as there should have been dots on eleven letters, there is a dot also on the 'Ayin' of "ad", to complete the eleven.

Da'as Zekenim #2 and Hadar Zekenim #2 (both citing Mesores ha'Gedolah): Ezra said, 'If Moshe will ask why I wrote these words, I will say "therefore, I put dots on them" (to show that they should be erased); whereas if he will agree with what I wrote, I will erase the dots. ³

Riva (citing R"M from Rottenberg): The dot on the 'Ayin' shows that liability for known sins would only take effect seventy days later - on the tenth of Nisan. ⁴

Sanhedrin 43b, #1 (according to R. Yehudah): They teach us that Yisrael were not punished for hidden transgressions until they crossed the Yarden (but for known ones they were punished even before that).

Sanhedrin 43b, #2 (according to R. Nechemyah): The simple meaning of the Pasuk is that we accept liability both for sins that only Hashem knows and for those that are revealed, ⁵ and the dot on the 'Ayin' of "Ad" indicates that only one of these is permanent - "Ad Olam" - is for known sins).

Rambam, Hilchos Yesodei ha'Torah, 9:3: To teach us that all the Mitzvos of the Torah apply at all times (and can never be negated). ¹ .