Bab. Talmud Pesachim 116b says that during the Seder, one begins with shame / humility and ends with praise. Meaning, that during the Magid section of the Seder, we begin with the "mood" of our humble history as slaves in Egypt, and end with praising G-d for our Exodus and Redemption.
The Mishnah states that we use the section from Deuteronomy (I lost part of my web connection, so would appreciate of someone can edit in the location.) beginning with the words ארמי אובד אבי
If the mitzvah on Pesach night is just to tell the story of the Exodus, why do we need any "theme" at all? What do the concepts of humility vs. praise have to do with telling the story of the Exodus?
If this theme is important or critical, aren't there other sections in the Torah that might accomplish the same job? (See next question, as an example)
The mitzvah is to tell the story of the Exodus. The section the Mishnah suggests seems like a round-about way to do this. ("Round-about in the method that we do it in the Haggadah. We recite verses then explain this by using proofs from other verses, the majority which are in Exodus. Why not just read those Exodus verses directly?) Why not read selected verses that talk about the 10 plagues (We do a bit of that in Maggid, anyway) from parshat Va'era and Bo, and perhaps some verses about the commandments of matzah and marror (like we recite in the Rabban Gamli'el part) and, maybe end with some verses surrounding the story of the Splitting of the Sea (more than the 1 or 2 verses that we recite related to Rav Akiva's sayings. etc.)?