You shall tell it to your child. One might have thought that one should do so from Rosh Hodesh: This passage is not a continuation of the previous one. The father is not addressing his son who doesn’t know how to ask here. Rather the author of the Haggadah offers another explanation for Exodus 13:8. It is an explication of when we are obligated 'to expand on' the story of the Exodus. We might presume that one is obligated to expound on the teachings of Passover from the beginning of Nisan, since God told Moses, "This month shall be unto you the beginning of months…." Just as Moses began warning the people of the coming observance on Rosh Hodesh, so too, we might think we should begin explaining the Exodus from Rosh Hodesh. Therefore the verse adds "on that day," to teach us that it applies not on Rosh Hodesh but from the day when Israel was redeemed from slavery. We might also presume that one is obligated to expound on the teachings of Passover from the day before Passover when the sacrifice was slaughtered since it says 'On that DAY.' The phrase adds, "Because of this," teaching us that we only expound when the offering is brought before us; that is, when he can point at the matzah and the maror, identifying them with the word "This." It was necessary to teach this because previously Scripture states: "Seven days you shall eat matzot" (Ex. 13:7) and "on the evening you shall eat matzot." (Ex. 12:18). Since the end of the verse is, "God did this for me when I went forth from Egypt," (Ex. 13:8) it was necessary to clarify when we are to tell the story since we eat matzah all week.

Another explanation: "Because of this (zeh) which the Lord did for me…" The Gematria of the word zeh is twelve because a person performs twelve mitzvot on Seder night. They are: four cups of wine, haroset, karpas, washing ones hands twice, motzi, matzah, maror and the sandwich. In the time of the Temple when the Passover offering, the matzah and the maror were brought, they would point at them and say, "Because of this which the Lord did for me."