What is the tachlis of the Seder Night? In short it is to fulfill the words of the Ramban at the end of Parshas Bo.
שאין לך אדם שיש לו חלק בתורת משה םלוכש ונירקמו ונירבד לכב ןימאנש דע תווצמה השעי םא אלא דיחיב ןיב םיברב ןיב םלוע לש וגהנמו עבט םהב ןיא םיסנ כי םהילע רובעי םאו ורכשר ןוילע תריזגב לכה ושנע ונתי
What comes out of his words is that by the end of the night we must believe in Hashgacha Peratis and Kelalis and that even all nature is supernatural by the will of Hashem. Otherwise one has no place in Toras Moshe Rabbeinu.
In order to attain this emunah we have the mitzvah of סיפור יציאת מצרים. For it is the passuk (Tehillim 117 10) האמנתי כי אדבר I came to believe because I spoke about it, demonstrates וכל המרבה לספר הרי זה משובח the more one speaks about Hashem and his miracles like those of Yetzias Mitzrayim he will come to believe that everything in the world is truly supernatural created and appointed by the desire of the Ribbono Shel Olam.
Siman Nirtzah and Moshe Rabbeinu
The last Siman is נרצה we should become desirable through our Seder to Hashem and to Moshe Rabbeinu. For as our sefarim tell us נרצה is gematriah משה. Even though Moshe is mentioned once throughout the Haggadah "by the way" in the passuk ודבע השמבו 'הב ונימאיו, he is hinted in the Siman נרצה. This follows a pattern of Moshe not being mentioned in Parsha Tetzveh however he is hinted in the number of 101 pessukim with the hidden letters of his name .מ ם שין הא However, here it is much deeper. The tachlis of the Seder as we mentioned above is to believe in all the miracles of Yetzias Mitzrayim and those in every day life. The Ramban if one fails to do so then he has no portion in the Toras Moshe. One must also believe in Moshe as Hashem's prophet which they did at Kerias Yam Suf ויאמינו בה' השמבו עבדו. The Siman Nirtzah is to beseech Hashem that we should be desirable to Him and thereby have a portion in Torah Moshe which is also part of the tachlis.
Why Mention the Giving of the Torah at Maggid?
אוה ךורב םוקמה ךורב This is the reason why at the beginning of Maggid we say םוקמה ךורב לארשי ומעל הרות ןתנש אוה ךורב. Why is the giving of the Torah mentioned at the beginning of Magid? To let us know that this is the mission goal of tonight to ascertain that one has a portion in Moshe Rabbeinu's Torah. This is because Torah is one of the three things that is acquired through the suffering received in the bondage of Mitzrayim.
