The Gemara says that Pinchos was the: מָ שוּחַ מִלְׂחָמָה Cohen who went to war. He was a warrior, and his job was to encourage Klal Yisroel in battle; that they should have Bitachon and not be afraid of war. This is exactly what Dovid did, since he was an example of Bitachon for Klal Yisroel when he went to war. The Gemara says that Pinchos went to war against the Midyanim to avenge his Zeide, Yosef, who was sold by them as a slave. The Maharal explains that Midyan gloried in unbridled lust and desire.
Yosef’s defining characteristic was his ability to conquer and channel desire. Selling him symbolized the triumph of impurity over holiness. Pinchos embodied the spirit of his great ancestor, Yosef (end quote Maharal). The Maharal also says that when Golyas stood up against Hashem, it was an outgrowth of his mother Orpah’s wickedness in her extreme promiscuity.
So when Dovid killed Golyas it was a victory of Kedusha over Tum’ah, which was exactly the Tachlis of Pinchos and he battles against Midyan and Zimri. The very first appearance of Dovid in Tanach and Pinchos in Chumash are strikingly similar in so many ways. Both are a war of Kedusha against Tum’ah (Zimri and Golyas). Both episodes had obstacles; Eliav trying to stop Dovid, and the Yidden trying to stop Pinchos.
