Let's pull together some things we already pointed out.
First, the Wise Son as we see him in Deuteronomy is asking a question about the entire Torah. We pointed out that the notion of wisdom expressed by the Wise Son is based on a fundamental awe of God. We understand that the seeking of wisdom is a sign of wisdom itself. And we understand that the Wise Son perceives the importance of community.
All of these reasons together could be the basis for the M'chilta speaking about the Wise Son first. Moreover, his question introduces us to some of the most basic and desirable elements of the Torah. His question invites us to discuss all aspects of Torah, from the simplest point to the loftiest concept.
Or, another way to think about it is maybe the reason we kick off with the Wise Son is because he is the archetype we would most like to emulate.
For that reason, speaking about the Wise Son draws us in immediately. If we are actual parents, this is the child we may want our own children to be: Respectful, inquisitive, a child of faith and conscious of others.
As a kid, I remember the Wise Son as being the part of the haggadah that all of us wanted to read (we kids took turns reading different sections—since I was youngest, I usually got stuck with the One Who Doesn't Know to Ask
Knowing as we do that the Wise Son of the Torah is asking about the entire Torah, how do Chazal come to place him (and the other Sons) at the seder table? And even if we do have reason to bring them into that context, why did Chazal change the answers given to the Sons from the answers given in the Torah?
The inspiration may, in fact, originate with the Wise Son.
Here is the passage from the Torah with the question and the answer:
דברים ו(כ) כִּֽי־יִשְׁאָלְךָ֥ בִנְךָ֪ מָחָ֖ר לֵאמֹ֑ר מָ֣ה הָעֵדֹ֗ת וְהַֽחֻקִּים֙ וְהַמִּשְׁפָּטִ֔ים אֲשֶׁ֥ר צִוָּ֪ה יְקֹוָ֥ק אֱלֹהֵ֖ינוּ אֶתְכֶֽם:
(כא) וְאָמַרְתָּ֣ לְבִנְךָ֔ עֲבָדִ֪ים הָיִ֥ינוּ לְפַרְעֹ֖ה בְּמִצְרָ֑יִם וַיֹּצִיאֵ֧נוּ יְקֹוָ֪ק מִמִּצְרַ֖יִם בְּיָ֥ד חֲזָקָֽה:
(כב) וַיִּתֵּ֣ן יְקֹוָ֡ק אוֹתֹ֣ת וּ֠מֹפְתִים גְּדֹלִ֨ים וְרָעִ֧ים׀ בְּמִצְרַ֪יִם בְּפַרְעֹ֥ה וּבְכָל־בֵּית֖וֹ לְעֵינֵֽינוּ:
(כג) וְאוֹתָ֖נוּ הוֹצִ֣יא מִשָּׁ֑ם לְמַ֙עַן֙ הָבִ֣יא אֹתָ֔נוּ לָ֤תֶת לָ֙נוּ֙ אֶת־הָאָ֔רֶץ אֲשֶׁ֥ר נִשְׁבַּ֖ע לַאֲבֹתֵֽינוּ:
(כד) וַיְצַוֵּ֣נוּ יְקֹוָ֗ק לַעֲשׂוֹת֙ אֶת־כָּל־הַחֻקִּ֣ים הָאֵ֔לֶּה לְיִרְאָ֖ה אֶת־יְקֹוָ֣ק אֱלֹהֵ֑ינוּ לְט֥וֹב לָ֙נוּ֙ כָּל־הַיָּמִ֔ים לְחַיֹּתֵ֖נוּ כְּהַיּ֥וֹם הַזֶּֽה:
(כה) וּצְדָקָ֖ה תִּֽהְיֶה־לָּ֑נוּ כִּֽי־נִשְׁמֹ֨ר לַעֲשׂ֜וֹת אֶת־כָּל־הַמִּצְוָ֣ה הַזֹּ֗את לִפְנֵ֪י יְקֹוָ֥ק אֱלֹהֵ֖ינוּ כַּאֲשֶׁ֥ר צִוָּֽנוּ:
Deuteronomy 6 (20) When your son will ask you tomorrow saying: “What are the testimonies and the statutes and the judgments that the Lord our God commanded you?” (21) And you will say to your son: “We were slaves to Pharaoh in Egypt and the Lord took us out of Egypt with a strong arm. (22) And the Lord gave us signs and wonders, great and bad, in Egypt with Pharaoh and with all his house before our eyes. (23) And He took us out from there in order to bring us to give to us the land which he swore to our fathers. (24) And the Lord commanded us to do all of these statutes to be in awe of the Lord our God for our good for all the days, to make us alive as on this day. (25) And it will be righteousness for us when we observe to do all of this commandment before the Lord our God as He commanded us.
The answer the Torah supplies fulfills in the most basic sense the mitzvah of haggadah, of telling our children about the going out of Egypt and its consequences.
Therefore, this passage pulls us to the seder table where we are enjoined to tell our children about the redemption from Egypt with all its myriad implications.
And now that we've said all that, perhaps we have the primary reason for why the Wise Son is mentioned first. It is his question in the Torah that provokes the answer which is, in essence, the haggadah itself.
Once we sit our Wise Son down at that table, though, things change.
Next time, we'll contrast how the Torah replies to the Wise Son with how the M'chilta replies.