by Moshe Burt
We learn that when Yithro had heard all that Hashem had done for B’nai Yisrael, he left Midian with Tzippora and Moshe’s two sons and went to join with the Jews.
We are not absolutely certain as to whether any one specific event Yithro heard boosted him to circumcize himself and to go out to join the B’nai Yisrael, and if so, which exact event it was, or whether it was the sum total of all he had heard which convinced him to become a Jew.
In the sefer Ner Uziel: Perspectives on the Parsha, Rabbi Uziel Milevsky z’l writes on our Parsha Yithro (p. 380-383) indicating that were Yithro to have come to join the Jews after Yetziat Mitziyim or after the cri’at Yam Suf, it would have been unlikely that he could have joined with the Jews due their concern as to what his motivations might be; i.e. whether he was anxious to be on a winning team, on the right side. It would seem to this author that this is not unlike many athletes who, when reaching free agency status, seek the best deal, to earn more than their peers, to join onto the team which has gone all-the-way. [...]