Rashi on Exodus 13:14/רש"י על שמות י״ג:י״ד

1כי ישאלך בנך מחר WHEN THY SON ASKETH THEE מחר — There is a usage of the word מחר that refers to “now” (i. e. to the period of time that is nearest to “now” viz., to-morrow), and there is another usage of מחר that refers to a day following after the lapse of some time, as, for example, this מחר here and as, for example, (Joshua 22:27) “That your children may not say to our children in time to come (מחר)” which occurs in the chapter about the sons of Gad and the sons of Reuben (Mekhilta).

2מה זאת WHAT IS THIS? — This is the question of a dull child who has not sufficient understanding to question very profoundly and who therefore asks in an indefinite fashion, “What is this?” In another passage (Deuteronomy 6:20) it states, “[When thy son asketh thee…], What mean the testimonies and the statutes and the judgments … [which the Lord our God hath commanded you?]” This, however, is the question of a wise son. The Torah in mentioning four different explanations of the Passover sacrifice-rite to be given by a father to his children, is speaking in reference to four different types of son: the wicked son (12:25 and in the second half of 13:8), and one who has not sufficient understanding how to ask (in the first half of 13:8), and one who asks in an indefinite manner (13:14), and one who asks in a wise fashion (Deuteronomy 6:20) (cf. Mekhilta; Jerusalem Talmud Pesachim 10:4).