We were slaves and our forefathers were idolaters

After reciting the mah nishtanah, we state that "we were slaves and now we are free." This follows Shmuel's explanation of the Mishnah (Pesachim 10:4) that the father answers the mah nishtanah by instructing his son by starting from a lowly state and moving to a high state.

The paragraph continues that even though we are wise, we still have to review the Exodus, and whoever reviews more of the story is to be praised. As noted, by Goldschmidt (p.17) the end of the paragraph is not connected to the beginning of the paragraph that "we were slaves and now we are free." Instead, the point of the end of the paragraph is that one must review more of the story. Afterwards we record two narratives from Tannaim that demonstrates this idea to review the story all night.

Afterwards, the Haggadah records the four sons and Rav's explanation of the Mishnah of our change in status, from idolaters to worshipping G-d. The four sons not mentioned in the Mishnah. Why are the four sons recorded in the Haggadah? Furthermore, even if they are mentioned, one would have thought that they would be recorded in conjunction with the mah nishtanah to join all the questions together. Furthermore, why is Rav's explanation of the Mishnah not juxtaposed with Shmuel's explanation?

Maybe the answer is that just as Shmuel's explanation of the change in status is after a set of questions, so too Rav's explanation of the change in status must also follow a set of questions. Thus, we first read about the four sons, and these are the questions prior to the statement "in the beginning our forefathers worshipped idols, and now we worship G-d." With regard to each son, there is short answer, but the answer of "in the beginning our forefathers worshipped idols, and now we worship G-d," is a general answer to all four sons. (Note, the paragraph of yachol is part of the response to the one who cannot ask, see Abarbanel.)

In both cases, the mah nishtanah and the four sons, we have four questions. By the mah nishtanah, we have one set of four questions, while by the four sons, each son asks one question. Furthermore, the types of question correspond to the answers of Rav and Shmuel. Shmuel's explanation of the changeover from a lowly status to a good status was a physical change, and the four question of the mah nishtanah refer to physical issues of eating and leaning. However, by the four sons, all the questions refer to the religious obligation of the people, and this corresponds to Rav's explanation of the changeover of the people as being a religious transformation. Thus, the general answer to all four sons is that we do all these actions because we worship G-d.

Finally, prior to the four sons we have the sentence, barukh hu, "Blessed be He" and similarly this phrase re-appears after we read the verses in the book of Yehoshua of the transformation of the people. According to Goldschmidt (p.22,38) both instances of the phrase are from the time of the Geonim. These two instances of the phrase "Blessed be He" serve as a bookend to the four sons and our statement that "in the beginning our forefathers worshipped idols, and now we worship G-d." They show that the four sons and the statement "in the beginning our forefathers worshipped idols, and now we worship G-d" are one unit.