זוהר ויקרא — דף ו ע”א

Rabbi Hiyya sat before Rabbi Shimon and asked him: why did the Torah enumerate the sons of Ya'akov? Rabbi Shimon answered that the holy names of the tribes correspond to the wings of the Divine Chariot (Merkava), and that is why the Torah enumerates them to reveal their secrets. The tribes correspond to the four directions and the secret of the Chariot.