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. Sefer Shemos, Perek 18, posuk 9 states “Vayichad Yithro” which Rashi renders as Yithro “rejoiced” at seeing B’nai Yisrael free of Mitzri bondage, at seeing K’riyat Yom Suf and at B’nai Yisrael’s victory over Amalek.
Why was it that Yithro sought to join B’nai Yisrael? We are not absolutely certain as to whether any one specific event Yithro heard triggered him to circumcize himself and to go out to join the B’nai Yisrael, or if there was one specific event, which exact event it was, or whether it was the sum total of all he had heard which convinced him to become a Jew.