The astrological sign for Sivan is Gemini, the twins. This alludes to the complexity necessary for learning the Torah, which was given in this month. The Torah comprises the Written Torah and the Oral Torah, and it was given to us in the third month, a time that reflects its complexity. This complexity ultimately leads to recognition of the unity [of the Torah].

Because Jacob [the third patriarch] is [designated by the sign Gemini, i.e., the] twins, the Torah was given to his children in the month [whose sign is] twins, and the Torah is the mystical concept of twins, namely, the Written Torah and the Oral Torah. It was given in the third month, to the nation of three [sections: priests, Levites, and Israelites], with the qualities of the three [patriarchs]. It is a threefold Torah: Torah, Prophets, and Writings. All this is one [i.e., the mystical concepts of twins, and of these groups of three, give rise to a unified view of everything]. (Zohar 2:78b)