There is a well known midrash that describes how when the Children of Israel stood poised by the Red Sea with the Egyptian army chasing them, the first person to jump in, thereby precipitating the splitting of the sea, was Nahshon ben Amminadav from the tribe of Yehuda. According to our Gemara, there is a difference of opinion as to whether this is what happened.
According to Rabbi Meir, the argument that took place on the shore of the Red Sea related to the fact that members of all of the different tribes wanted to be the first to jump into the water, and it was the tribe of Binyamin that succeeded in reaching the waters first. Rabbi Meir teaches that this act is what allowed the tribe of Binyamin to merit that the Temple was built within the boundaries of their shevet (tribe).
Rabbi Yehuda disputes this version of events, claiming that when the tribes were standing on the shore of the Red Sea, none of them wanted to throw themselves into the water until Nahshon ben Aminadav from the tribe of Yehuda did so. At that time Moshe was in the midst of prayer and God instructed him to pay attention to his people who were already in the water, and instruct the others to follow. Rabbi Yehuda teaches that the act of Nahshon was what allowed the tribe of Yehuda to merit the monarchy.
In the book Ben Yehoyada, Rabbi Yosef Hayyim mi-Baghdad’s work on the aggadic portions of the Talmud, the author points out that the reward granted to both Yehuda and Binyamin are eternal rewards – the Jewish people’s monarchy will always be from the house of King David, and the place of the Temple will always remain on Har HaBayit in Jerusalem. The Iyyun Ya’akov argues that both rewards contain an element of monarchy, since King Shaul, the first king of Israel, came from Shevet Binyamin.