Chad Gadya: The Kid and the Father
In response to some who ridiculed the Chad Gadya poem, the Baal Shem of Michelstadt wrote a commentary on it. The gadya, the kid, refers to Am Yisroel, who are hinted to in the midrash on Naso, where the twelve tribal leaders offer ten goats as a sacrifice to Hashem. The letters of gadya also stand for gimel, the three Patriarchs; dalet, the four Matriarchs; yud, the Ten Commandments; and alef, the Torah. The Abba is Our Father in Heaven, as it says, “Are you not our Father?” And He acquired us, as Chazal say in Avos: “Yisroel, one acquisition,” as it says in Shemos 15:16, “This people You acquired.” The two zuzim are plural and symbolize the two luchos given to Moshe twice: once before the sin of the golden calf and once again afterward.
Source: Peirush on Chad Gadya, Haggadah Shel Pesach (Baal Shem of Michelstadt, citing Olas Chodesh Nissan 5740)