Kabbalah of the Kaira (Seder Plate)
According to the Ari Zal (Rabbi Yitzchak Luria, ztz”l), the kaira represents the ten Sefiros.
The platter itself, when made of silver or gold, represents the sefira of Malchus (royalty). The three matzos, placed at the head of the kaira, represent the sefiros of Chochma (Logical Wisdom), Binah (Intuitive Understanding), and Da’as (Common Sense). On the upper right corner of the kaira is the zeroah (roasted lamb shank), which represents the sefira of Chesed (Kindness). On the upper left corner is the beitzah (roasted egg), which represents Gevurah (Strength). In the center of the kaira is the maror (horseradish), which represents the sefira of Tiferes (Beauty/Harmony). Tiferes is a blending of Chesed and Gevurah, perhaps like the maror which starts out sweet and turns bitter.1 The charoses, placed beneath the zeroah, represents Netzach (Victory). The karpas (romaine lettuce) represents the sefira of Hod (Majesty).
Why is the zeroah associated with Chesed and the beitzah with Gevurah? The Hebrew word zeroah reminds us of the zeroah netuya, the outstretched arm, the Divine Chesed that was shown to us, that brought us our salvation. The beitza is a traditional food of mourning, as the oval shape represents the circle of life with its ups and downs. The egg is associated with Gevurah, a time of loss, when there is a concealment of apparent kindness.
1. See Maror by Rabbi Yitzchak Gornish, Kosher Spirit, Pesach 5770.