The main part of haggadah is expansion of parsha of bikkurim, where we expound on the story of our journey to Mitrzayim and our redemption. The idea of starting with the negative difficulties and going through to the terrific ending does not just apply to our time in Mitzrayim. Rather, this is something that defines and presents an ongoing destiny of the Jewish people. Hashem promised us that He is committed to us no matter what, and our relationship is there for keeps. We will face many challenges through the 4 periods of exile, but Hashem will save us in every generation.