The Gemara in Sanhedrin 82b interprets the posuk in Bamidbar 25:13 to mean that the atonement Pinchas facilitated, is worthy of continuing to atone forever
The Holy One, Blessed be He, said to Moses: Be the first to greet Pinehas with a blessing of peace, to honor him before the people, as it is stated: “Therefore say: I hereby give to him My covenant of peace” (Numbers 25:12), and it is stated: “And it shall be unto him and to his descendants after him a covenant of eternal priesthood, because he was zealous for his G-d and he atoned for the children of Israel” (Numbers 25:13), and this atonement that he facilitated is worthy of continuing to atone forever.
The Ben Yehoyada (ad loc.) explains something along the lines that tzadikkim provide protection during their lives. In the case of Pinchas, he facilitated protection/atonement that would endure forever. Not only during Pinchas' life.
What does this Gemara mean when it says that "the atonement Pinchas facilitated is worthy of continuing to atone forever"?
I've seen most meforshim (on Bamidbar 25:13) explain the literal meaning of the "Bris Shalom" (covenant of peace), but I was not able to locate any meforshim describing the atonement Pinchas facilitated in light of this Gemara.