Why is this night called the Seder Night? The origins of this night go back to the event when Yaakov “stole” the berachos from Esav. There a few indications to this. Chazal say it was the night of the 15th of Nissan when this occurred. Yaakov took two goats, one for the Pesach and one for the korban chagigah. When Yitzchak told Esav that his brother came with “mirmah” he was referring to the fact that Yaakov fed him the Afikoman and therefore it is prohibited to eat afterwards. Since eating was a condition before he was able to give the berachos, he was now disabled to bless Esav. Rav Chaim Sonnenfeld hints to this interpretation with a gematriah that “mirmah” is equal to afikoman. This is why Onkeles translates here the word mirmah, which normally means trickery, to be with wisdom. A further indication that the berachos that Yaakov received from Yitzchak was on Pesach is from the fact that on Pesach we bench Tal the prayer for dew which was the first words of the beracha given to Yaakov veyiten lecha Elokim meeetal hashamayim. Even the minhag of a child “stealing” the afikomen and then asking for a reward or beracha originates with Yaakov taking the berachos through the Afikomen this very night.
Now that we have proven that this night finds its origins in Yaakov’s taking the berachos from Esav we can continue to explain why this night is called Seder. How are we supposed to understand this seemingly deceitful heisting of Esav's berachos by a Yaakov, who is the personification of truth and emes? According to simple understanding it is not explicable. However, on the levels of derush remez and sohd [homiletics, hints and kabbalah] it is clearly explainable with countless interpretations. אין אין אין הפסוק אומר אלא דרשוני)). Here is just a sampling of interpretations. When Yaakov said I am Esav your first born he said it with a pause as if there lay two statements, I am, Esav is your first born. Others interpret his statement to mean I am Esav meaning the person in your mind who is truly deserving of your berachos. In all reality, Esav would never have merited to these berachos because even Yitzchak said to Esav that it is Hashem who is bestowing the berachos and he is only serving as Hashem’s conduit. Being so, there was no possibility that Hashem would have agreed to give Esav the berachos anyway just as we find when Yaakov himself wanted to bless Ephraim and Menashe, the Shechina disappeared from it disabling him to bestow berachos on his grandchildren . In fact by deceiving his father into believing that he was Eisav, he accomplished that the berachos were at least given. For otherwise it would be quite possible that when Yitzchak would have shockingly discovered that all along Eisav was an imposter, he might have fallen into a depression which would not have allowed for prophecy or ruach hakodesh to come to him just as we found by Yaakov after being told of Yosef’s demise. So in reality, this night of Pesach which is a night of bestowing of berachos, can only be understood without pshat which is the simple understanding.
Even the simanim of the Seder themselves cannot be simply understood as is. Take the first two kadaish urechatz – sanctify and cleanse. The mefarshim ask should not the order be the opposite that one must first cleanse from sins and only then become holy? Yet we can answer this with the concept of the mefarshim who explain that we were redeemed 190 years earlier from Egypt because Hashem sanctified us to become his nation during makas bechoros. The rule in the Gemara is that hekdesh mafkiah meeday shibud. That if someone borrows money and the loaner thereby has a lean on the borrower’s property, the borrower is not permitted to sell and thereby makes the sale invalid. However if the borrower sanctifies his property upon which lies a lean to his loan, to the Beis Hamikdash, that transaction is valid. So too, Yisrael had a lean of servitude to Mitzrayim for another 190 years. However Hashem sanctified them to be His Hekdesh which thereby freed them from their previous obligation.