Why Moses Sent Jethro Home Before the Torah Was Given

What is written above in the matter, the portion of Jethro, what he teaches Moses, as it says, "And you shall select from all the people able men" and so forth (Exodus 18:21)? And afterward, "In the third month." Solomon said, "The heart knows its own bitterness" (Proverbs 14:10); therefore, "and a stranger does not share in its joy" (ibid.). The Holy One, blessed be He, said: Israel were enslaved in mortar and bricks in Egypt, while Jethro sat in his house quiet and secure, and now he comes to share in the joy of the Torah with My children! Therefore, "And Moses sent his father-in-law away" (Exodus 18:27), and afterward, "In the third month" and so forth (Exodus 19:1). Another interpretation: why so? Moses reasoned by an argument from minor to major. He said: if, regarding a single commandment, when the Holy One, blessed be He, came to give the commandment of the Passover offering, He said, "No foreigner shall eat of it" (Exodus 12:43), now that He is coming to give the whole Torah to Israel, shall Jethro be here and witness it with us? Therefore, "And Moses sent his father-in-law away" and so forth (Exodus 18:27), and afterward, "In the third month" (Exodus 19:1).