וְהִגַּדְתָּ֣ לְבִנְךָ֔ בַּיּ֥וֹם הַה֖וּא לֵאמֹ֑ר בַּעֲב֣וּר זֶ֗ה עָשָׂ֤ה יְהוָה֙ לִ֔י בְּצֵאתִ֖י מִמִּצְרָֽיִם׃
E tu contarás ao teu filho naquele dia, dizendo: Por causa disto Hashem fez por mim, quando saí de Mitzrayim.
Tiferet Shlomo
"You pour the cup and hear the son asks what..." (Hagadah): This hints to the fact that the night is called the Second Level of Greatness [a kabbalisitic concept], and this is the level of the question of the father to the son (and then it returns because Hashem's kindness is everlasting).