Why Moses Went Back to Jethro Before Returning to Egypt

(Exodus 4:18-19) "And the LORD said to Moses in Midian." It is taught: one who has vowed not to derive benefit from his fellow may be released from the vow only in his presence. From where are these matters derived? Rav Nachman said: as it is written, "And the LORD said to Moses in Midian" — He said to him, "In Midian you vowed; go and annul your vow," as it is written, "And Moses consented [vayyo'el] to dwell" (Exodus 2:21), and alah means nothing other than an oath, as it is written, "and he brought him under an oath [be'alah]" (Ezekiel 17:13), and it is written, "and he also rebelled against King Nebuchadnezzar, who had made him swear by God." Rabbi Eliezer says: one may open [a way to annul a vow] by an unforeseen development, but the Sages forbid it. How so? If one said, "I shall derive no benefit from so-and-so," and then that man became a scribe, or was marrying off his son, and the vower said, "Had I known that he would become a scribe, or that he would soon marry off his son, I would not have vowed." What is the reason? Rav Chisda said: because Scripture states, "for all the men are dead" (Exodus 4:19) — but this death was an unforeseen development; from here we learn that one may open with an unforeseen development. And the Rabbis, what is their reason? They hold that those men had not actually died, for the Master said: wherever it is said "contending" or "standing," it refers to none other than Dathan and Abiram; rather, they had come down from their wealth. "And Moses went and returned to Jether his father-in-law" — it need only have said, "and he returned to Egypt," so why did he return to Jethro? To annul his vow. What did the Holy One, blessed be He, do? He bound a cloud there, and, as it were, He annulled the vow of Moses.