The Daily Ma’amar of our Rebbe Rav Eliezer Berland shlit”a, courtesy of the “Hashem Hu HaElokim” leaflet:
Because the secret of the Karpas which we eat at the beginning of the seder of seder night, its role is to draw the green line, which is the sefirah (Divine emanation) of Binah (Understanding), which encircles the whole world. That this is the secret of “Esther was of a greenish [complexion]” (Likutey Moharan 12).
Because “Esther Kadmon (Primordial Esther)” is the numerical value of “Rosh Hashanah” = 861, because Esther was a soul from Adam Kadmon, in the secret of “And their remembrance shall not perish from their descendants” (Esther 9:28), as it is said about the Yesod (Foundation) of Aba (Hochmah-Wisdom) which receives its illumination from Adam Kadmon, and breaks through the Yesod of Ema (Binah) and the Yesod of Zeir Anpin (the “Small Face”) and the Yesod of Rachel, that this is the secret of spreading out the letter [the scroll] of Purim.
Because through the eating of the Karpas, we merit to the garments of Karpas, because through eating the the Karpas, we merit to the revelation of the glory of His kingdom, as it is said, “There were [hangings of] white, fine cotton (karpas), and turquoise wool, held with cords of fine linen and purple wool, upon silver rods and marble pillars; the couches of gold and silver were on [a pavement of] variegated marble” (ibid. 1:6).
Because the Karpas alludes to the Sefirah of Malchut (Kingship), when it is still a point under the Yesod of Zeir Anpin and from behind it, and little by little, Malchut is grown through the recitation of the Hagadah, and the story of the miracles and wonders, until we reach the blessing “HaMotzi Lechem Min Ha’aretz.” Then the Karpas, which is Malchut, is grown from behind Zeir Anpin to the whole stature of Zeir Anpin, until it reaches Keter (Crown) opposite Keter, from behind. Now in the blessing “HaMotzi Lechem Min Ha’aretz,” she turns around face-to-face, and is grown, and is grown through the blessing “HaMotzi Lechem Min Ha’aretz” — the Keter of Rachel opposite Tiferet (Beauty) of Zeir Anpin, and Rachel continues to grow face-to-face.
And in the blessing “Al Achilat Matzah,” Rachel already is grown Keter opposite Hochmah of Zeir Anpin, and in the blessing “HaKorech Matzah im Maror,” Rachel already is grown and her Keter has grown opposite the Keter of Zeir Anpin, face-to-face, and the unification of face-to-face will be in the two blessings “Al HaGefen” over the wine. Therefore, between the third and fourth [cup], don’t interrupt.
And then we merit to the fifth cup of “V’heiveiti (I will bring),” that this is the secret of the building of the Third Temple, which will be a Temple of fire, and about this it is said “A good eye is blessed” (Mishlei 22:9), that we merit to “It shall be good in Your eyes to bless all Your people Israel with abundant strength and peace.”
Then there will be the wondrous peace of “The wolf will live with the sheep, and the leopard will lie down with the kid; and a calf, a lion whelp and a fatling [will walk] together, and a young child will lead them. A cow and a bear will graze and their young will lie down together; and a lion, like cattle, will eat hay. A suckling will play by a viper’s hole; and a newly weaned child will stretch his hand toward an adder’s lair. They will neither injure nor destroy in all of My sacred mountain; for the earth will be as filled with knowledge of Hashem as water covering the sea bed” [Yeshaya 11:6-9].