וַיִּגְדַּ֥ל הַיֶּ֖לֶד וַיִּגָּמַ֑ל וַיַּ֤עַשׂ אַבְרָהָם֙ מִשְׁתֶּ֣ה גָד֔וֹל בְּי֖וֹם הִגָּמֵ֥ל אֶת־יִצְחָֽק׃ וַתֵּ֨רֶא שָׂרָ֜ה אֶֽת־בֶּן־הָגָ֧ר הַמִּצְרִ֛ית אֲשֶׁר־יָלְדָ֥ה לְאַבְרָהָ֖ם מְצַחֵֽק׃ וַתֹּ֙אמֶר֙ לְאַבְרָהָ֔ם גָּרֵ֛שׁ הָאָמָ֥ה הַזֹּ֖את וְאֶת־בְּנָ֑הּ כִּ֣י לֹ֤א יִירַשׁ֙ בֶּן־הָאָמָ֣ה הַזֹּ֔את עִם־בְּנִ֖י עִם־יִצְחָֽק׃ וַיֵּ֧רַע הַדָּבָ֛ר מְאֹ֖ד בְּעֵינֵ֣י אַבְרָהָ֑ם עַ֖ל אוֹדֹ֥ת בְּנֽוֹ׃ וַיֹּ֨אמֶר אֱלֹהִ֜ים אֶל־אַבְרָהָ֗ם אַל־יֵרַ֤ע בְּעֵינֶ֙יךָ֙ עַל־הַנַּ֣עַר וְעַל־אֲמָתֶ֔ךָ כֹּל֩ אֲשֶׁ֨ר תֹּאמַ֥ר אֵלֶ֛יךָ שָׂרָ֖ה שְׁמַ֣ע בְּקֹלָ֑הּ כִּ֣י בְיִצְחָ֔ק יִקָּרֵ֥א לְךָ֖ זָֽרַע׃ וְגַ֥ם אֶת־בֶּן־הָאָמָ֖ה לְג֣וֹי אֲשִׂימֶ֑נּוּ כִּ֥י זַרְעֲךָ֖ הֽוּא׃ וַיַּשְׁכֵּ֣ם אַבְרָהָ֣ם ׀ בַּבֹּ֡קֶר וַיִּֽקַּֽח־לֶ֩חֶם֩ וְחֵ֨מַת מַ֜יִם וַיִּתֵּ֣ן אֶל־הָ֠גָ֠ר שָׂ֧ם עַל־שִׁכְמָ֛הּ וְאֶת־הַיֶּ֖לֶד וַֽיְשַׁלְּחֶ֑הָ וַתֵּ֣לֶךְ וַתֵּ֔תַע בְּמִדְבַּ֖ר בְּאֵ֥ר שָֽׁבַע׃ וַיִּכְל֥וּ הַמַּ֖יִם מִן־הַחֵ֑מֶת וַתַּשְׁלֵ֣ךְ אֶת־הַיֶּ֔לֶד תַּ֖חַת אַחַ֥ד הַשִּׂיחִֽם׃ וַתֵּ֩לֶךְ֩ וַתֵּ֨שֶׁב לָ֜הּ מִנֶּ֗גֶד הַרְחֵק֙ כִּמְטַחֲוֵ֣י קֶ֔שֶׁת כִּ֣י אָֽמְרָ֔ה אַל־אֶרְאֶ֖ה בְּמ֣וֹת הַיָּ֑לֶד וַתֵּ֣שֶׁב מִנֶּ֔גֶד וַתִּשָּׂ֥א אֶת־קֹלָ֖הּ וַתֵּֽבְךְּ׃ וַיִּשְׁמַ֣ע אֱלֹהִים֮ אֶת־ק֣וֹל הַנַּ֒עַר֒ וַיִּקְרָא֩ מַלְאַ֨ךְ אֱלֹהִ֤ים ׀ אֶל־הָגָר֙ מִן־הַשָּׁמַ֔יִם וַיֹּ֥אמֶר לָ֖הּ מַה־לָּ֣ךְ הָגָ֑ר אַל־תִּ֣ירְאִ֔י כִּֽי־שָׁמַ֧ע אֱלֹהִ֛ים אֶל־ק֥וֹל הַנַּ֖עַר בַּאֲשֶׁ֥ר הוּא־שָֽׁם׃
ויגמל AND HE WAS WEANED — at the end of twenty- four months (Gittin 75b).
At a juncture in Jewish history, the role of Yishmael is unclear despite the primary role of Yitzchak. The expulsion of Yishmael solidifies Yitzchak being the sole inheritor of the Brit Bein h'Bitarim. G-d now reinforces with Avraham that it is through Yitzchak that Avraham's legacy. The birth of Yitzchak marked the arrival of an appropriate receptacle for the legacy of Avraham. Therefore, the 400-hundred-year count starts with the Yitzchak's birth. The gematria accounted of 210 accounts for the 210 years that Avraham's descendants were enslaved in Egypt.
Yitzchak's second birthday, being weaned, represents an important inflection point in the endurance of Avraham's influence on the world. Yitzchalk's viability reaches an important milestone of sufficence. On Pesach, Avraham's guests, including Shem and Ever, celebrated the spiritual inheritor of Avraham, the first step in the development of the Jewish nation on Pesach. Without Yitzchak, Avraham's impact on civilization would be fleeting. Yishamel did not absorb Avraham's teachings, as evidenced by his play with Yitzchak, and, therefore, would not spread Avraham's teachings and influence. The impact of the Egyptian is removed from the upbringing of Yitzchak. Until Yishmael demonstrated bad character traits, Sarah did not have a problem with Yishmeal. Sarah recognizes the importance of bringing up Yitzchak without external influences. Hagar and Yishmael are sent out with bread, which would have been matzah and water. Rashi notes that the verse specifically excludes gold and silver. This early Passover served to foreshadow the events in Egypt and the development of a nation that carries on the legacy of Avraham.