Deuteronomy 29:28

The secret things are manifest before the Lord our God, and He will take vengeance for them; but the things that are revealed are delivered unto us and to our children for ever, to perform by them the thing that is right, for the confirmation of all the words of this law.

the hidden matters … that is, if someone practices idolatry in secret,

it is for God our God — meaning, his judgment will be at the hand of God , Who will punish him; but if it be public, then we, and our descendants, are obliged to do what is written in the Torah. (Some have interpreted the verse as follows: “The hidden matters are for God our God, and the revealed matters. It is only for us to act according to the words of the Torah.” But this interpretation contains a non sequitur. What would be the point of mentioning it, in this context?) Having previously said that God “cast them into another land”, Scripture now proceeds to say, “but if you return to God , even though you be outside the Land of Israel, God will restore your exiles.” Rabbi Y e hudah ben David Ḥayyuj, the grammarian, is of the opinion that the first instance of the word “restore” means “grant rest”. The sense of the verse is: “He will provide respite to the captives, and grant them mercy; afterward, he will send them back, and gather them …”.

THE SECRET THINGS BELONG UNTO THE ETERNAL OUR G-D. In the opinion of the commentators the verse states: “It is for the Eternal our G-d to execute judgment upon those who worship idols secretly, for all hidden matters are revealed before Him, but the things that are revealed are upon us and our children that we may do to them all the words of this Law — to smite the idol-worshippers in accordance with the law of the Torah. According to the interpretation of the Rabbis, too, it is so.
By way of the simple meaning of Scripture it is my opinion that the secret things are the sins that are hidden from those who commit them, as it is stated, Who can discern errors? Cleanse Thou me from hidden faults. The verse states: “[Our] hidden sins belong to G-d alone; for them we bear no guilt for having transgressed [unknowingly]. But the things that are revealed, namely our conscious sins, belong unto us and to our children forever, that we may do all the words of this Law as an eternal statute. As such we accepted it, obligating the one who was present [when the covenant was made] and the one who was not present. And because he included in the imprecation [the obligation] to perform all the commandments, he excluded from the ban whoever commits a sin unintentionally, so that he should not be afflicted by this curse. The words of Onkelos indicate this, for he rendered it, “The secret things are before the Eternal our G-d,” [thus implying that we will not be punished for sins we have committed unknowingly], but if he agreed with the [aforementioned] interpretation of the commentators [that it is for G-d to punish conscious sins committed secretly] then Onkelos should have said, “The secret things are ‘to’ the Eternal our G-d” [to punish].

הנסתרות לה' אלוקינו, I have already explained this on Deut. 27,15 in connection with the curses pronounced at Mount Gerizim and Mount Eyval. It is precisely because sins committed in secret cannot be dealt with by the courts, that the Torah has to go on record that the sinner will still not get away with his sin.

לנו ולבנינו עד עולם, it is up to us to administer the penalties prescribed by the Torah subject to the offender being convicted on the basis of reliable witnesses.

הנסתרות לה' אלוקינו, even though I have said that all of you are standing in the presence of the Lord whom it is impossible to mislead and deceive, so that He will collect His dues from everyone who owes him, G’d collects directly only from those whom it is not possible for His appointed representatives, i.e. a legally constituted judiciary to bring to justice.

והנגלות לנו ולבננו עד עולם, however, any sins committed publicly must be dealt with by this judiciary, forever, [I suppose the words עד עולם mean that there is no statute of limitations as in gentile countries. Ed.] לעשות את כל דברי התורה הזאת, to avenge G’d‘s having been slighted by the public commission of violations of Torah law, especially those affecting other people directly.

הנסתרות לה' אלוקינו, “concealed acts concern the Lord our G–d;” seeing that the Torah had written in verse 20 of our chapter that G–d singles out individual sinners for retribution,” and verse 21 sounds as if the sins of a single individual could cause G–d to react angrily against the whole people, or at least against a whole family all on account of that single rebellious Jew, Moses now reassures the people that precisely because He is omniscient and knows what goes on in the hearts of each one of us, He will deal with the individual who is guilty and not engage in punishing the innocent as “collateral damage.” However, sins committed openly, and ignored by the judiciary, thereby constituting collective guilt by the people who had appointed corrupt judges, will become the subject of what for the uninitiated looks like collective punishment. In fact, the retribution for openly committed sins and tolerated by the courts, will result in the punishment extending beyond a single generation as long as we do not wipe out the phenomenon of open rebellion against the covenant that the whole people had voluntarily entered into with Hashem. The Talmud in tractate Sanhedrin, folio 43 points out that the dots above the letters לנו ולבנינו and above the letter ע of the word עד, are to inform us that as long as the Israelites had not crossed the river Jordan and been on sacred ground, G–d had not punished anyone for sins committed in private, not witnessed by even family members. The reason for this was that only after crossing the Jordan did the Jews accept the Torah [most of whose commandments did not apply outside the Holy land. Ed.] individually and collectively, so that each Israelite became responsible also for the sins committed by his fellow Jew. At that point what is written the words לנו ולבנינו, “for us and our children,” became applicable. If you were to query that if the above were correct, why is the last dot on the word על instead of on ה' אלוקינו, perhaps the reason is that it would be inappropriate to do this when it is subject to being erased. The words: lashem elokeynu in Hebrew including the tetragram that I cannot spell out here, comprise eleven letters, and that is why our sages place 11 dots to hint to us that this is where the dots really should have been. [Since no Israelite who had not yet crossed the river Jordan ever saw a Torah scroll with these eleven dots, I find the interpretation offered quite irrelevant. Ed.] According to a text known as massoret hag’dolah, the dots are attributed to when Ezra had to rewrite the Torah after the redemption when different scrolls had variations in the text, and the time would come when Moses would challenge him why he had not done it differently, he would explain that because of his doubts he had placed the dots on top. If Moses would be satisfied with the way Ezra had done it, it would be easy to erase the dots without harming the text of the Torah scroll. From this it is clear that Ezra had his doubts about G–d not holding us responsible for not interfering when becoming aware of sins committed prior to crossing the Jordan.