The Haftorah of Parshas Tazria is the story of Na’aman, the Gentile general of the King of Aram. He had Tzaraas and could not find a cure for his condition. He came to the Prophet Elisha seeking help. Elisha told him, “Go immerse in the Jordan River.” Na’aman dipped himself in the Yarden. Lo and behold, his Tzaraas was cured. This is the story of Chapter 5 in Melachim II.
The Rokeach, an early Biblical commentary asks: Where did Elisha get the idea that the way for Na’aman to cure himself from Tzaraas would be to immerse in the Yarden?
The Rokeach says that there are three—and only three—pesukim in the entire Torah that both begin with the letter Nun and end with the letter Nun. The first pasuk is “Nega Tzaraas, when it will be found in man, he shall be brought to the Kohen.” [Vayikra 13:9]. The second pasuk is “Navi from your midst amongst your brethren like myself shall the L-rd your G-d raise up, to him you shall listen (tishma’un)” [Devorim 18:15]. The third pasuk is “Nachnu (we) shall cross over armed, before Hashem, to the land of Canaan, and ours shall be the heritage of our inheritance across the Jordan.” [Bamidbar 32:32]. Those are the only three pesukim in all of Chumash that both begin and end with the letter Nun. One is about Tzaraas; one is about a prophet; and one is about the Yarden.
The Rokeach says this was Elisha’s insight: The three pesukim reference a Metzorah (Na’aman), a prophet (Elisha), and the Yarden. The clear message is that the prophet should tell the Metzorah to immerse in the Yarden.