Why does Moshe tell the people that they witnessed the giving of the Torah and miracles in Egypt?

Question

In Sefer Devarim, Moshe Rabbeinu, in his last speech to the Jewish people, seems to constantly tell the Jewish people that they themselves witnessed the miracles and G-dly revelations. For example:

Devarim 4:9:

But beware and watch yourself very well, lest you forget the things that your eyes saw, and lest these things depart from your heart, all the days of your life, and you shall make them known to your children and to your children's children,

רַק הִשָּׁמֶר לְךָ וּשְׁמֹר נַפְשְׁךָ מְאֹד פֶּן תִּשְׁכַּח אֶת הַדְּבָרִים אֲשֶׁר רָאוּ עֵינֶיךָ וּפֶן יָסוּרוּ מִלְּבָבְךָ כֹּל יְמֵי חַיֶּיךָ וְהוֹדַעְתָּם לְבָנֶיךָ וְלִבְנֵי בָנֶיךָ:

10 the day you stood before the Lord your God at Horeb, when the Lord said to me, "Assemble the people for Me, and I will let them hear My words, that they may learn to fear Me all the days that they live on the earth, and that they may teach their children.

יוֹם אֲשֶׁר עָמַדְתָּ לִפְנֵי יְהֹוָה אֱלֹהֶיךָ בְּחֹרֵב בֶּאֱמֹר יְהֹוָה אֵלַי הַקְהֶל לִי אֶת הָעָם וְאַשְׁמִעֵם אֶת דְּבָרָי אֲשֶׁר יִלְמְדוּן לְיִרְאָה אֹתִי כָּל הַיָּמִים אֲשֶׁר הֵם חַיִּים עַל הָאֲדָמָה וְאֶת בְּנֵיהֶם יְלַמֵּדוּן:

Or Devarim 7:19:

The great trials that your eyes saw, the signs, the wonders, the mighty hand, and the outstretched arm with which the Lord, your God, brought you out. So will the Lord, Your God, do to all the peoples you fear.

הַמַּסֹּת הַגְּדֹלֹת אֲשֶׁר רָאוּ עֵינֶיךָ וְהָאֹתֹת וְהַמֹּפְתִים וְהַיָּד הַחֲזָקָה וְהַזְּרֹעַ הַנְּטוּיָה אֲשֶׁר הוֹצִאֲךָ יְהֹוָה אֱלֹהֶיךָ כֵּן יַעֲשֶׂה יְהֹוָה אֱלֹהֶיךָ לְכָל הָעַמִּים אֲשֶׁר אַתָּה יָרֵא מִפְּנֵיהֶם:

However, from Bamidbar 26:63-65 we see that all the censused men who left egypt had already died, and this was a new generation:

This was the census of Moses and Eleazar the kohen, who counted the children of Israel in the plains of Moab, by the Jordan at Jericho.

אֵלֶּה פְּקוּדֵי משֶׁה וְאֶלְעָזָר הַכֹּהֵן אֲשֶׁר פָּקְדוּ אֶת בְּנֵי יִשְׂרָאֵל בְּעַרְבֹת מוֹאָב עַל יַרְדֵּן יְרֵחוֹ:

Among these there was no man who had been [included] in the census of Moses and Aaron when they counted the children of Israel in the Sinai desert.

וּבְאֵלֶּה לֹא הָיָה אִישׁ מִפְּקוּדֵי משֶׁה וְאַהֲרֹן הַכֹּהֵן אֲשֶׁר פָּקְדוּ אֶת בְּנֵי יִשְׂרָאֵל בְּמִדְבַּר סִינָי:

For the Lord had said to them, "They shall surely die in the desert," and no one was left of them but Caleb the son of Jephunneh and Joshua the son of Nun.

כִּי אָמַר יְהֹוָה לָהֶם מוֹת יָמֻתוּ בַּמִּדְבָּר וְלֹא נוֹתַר מֵהֶם אִישׁ כִּי אִם כָּלֵב בֶּן יְפֻנֶּה וִיהוֹשֻׁעַ בִּן נוּן:

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Now we know that anyone who was younger than 20 at the time of the first census did make it into the Promised Land (Bamidbar 14:29). It is understood from there that anyone who was above 60 at the time of the first census also made it into the land (see also Rashi Bamidbar 14:33). The women also didn't die in the desert, nor did the Levites.

All that notwithstanding, ~600,000 men had died and were replaced with a new generation, at least half of which had not been born at the time of the exodus (anyone of the censused men between 20 and 40 at the time of Moshe's speech would have been born afer the exodus from Egypt).

If so, why did Moshe tell them all that they personally witnessed the events such as the giving of the Torah?

It seems weak to answer that Moshe was talking to the majority, even though a substantial portion had not themselves witnessed the events.

Answer 1

Rav Hirsch points out in his commentary on Devarim 4:9 that just as the entire nation saw the revelation, and just as this is a unique tradition of every person in the nation, must be passed as an everlasting witness from fathers to children, so to is it reagarded as each generation is to consider it as if each individual of that generation was there and saw the divine revelation. Every person has seen the miracles of the man and the well and the ananei hakovod. It is to be

the fundamental thought of each succeeding generation.

and indeed it applies to us today as well.

that what was received by the first generation is to be kept as closely and handed down so faithfully that the tradition takes the place of what had been personally experienced, and makes the very last grandson in duty bound to keep the Torah faithfully as if he had indeed received it himself at Sinai.

Answer 2

The Tiferet Yisroel, in his commentary to Avot 3:8, in explaining how Devarim 4:9 teaches us that the Scripture tells us that one who forgets something he learned has put his life in danger, explains the verse as follows (loose translation):

You can't say the verse is refering to the physical witnessing of the great miracles that were done in the desert, because the Torah was given to all the Jews [of all generations], and the later generations did not see the miracles. Therefore, the "seeing" that is mentioned in the verse refers to intellectual seeing [i.e. understanding], and is telling us that the things that you saw intellectually [i.e. learned], guard yourself from forgetting them.