And the plague stopped

"Pinchas Ben Elazar Ben Aaron HaCohen Hayshiv Es Chamosi Mai'al Bnei Yisroel"; "Pinchas, son of Elazar, son of Aaron the Kohen, turned back my anger from upon the Bnei Yisroel" Instead of saying "Hayshiv"- "turned back" my anger - it should have said "Bateil"- "nullified"?
Dovid HaMelech says in Tehillim,"Pinchos arose and executed judgment and the plague stopped. It was counted to him "LiTzdakah"- as a righteous deed - for all generations forever." What does the act of Pinchas have to do with Tzdakah?
The Vilna Gaon answers, according to the Torah every Jew is obligated to give annually a Machatzis HaShekel - a half Shekel- for the purchase of Korbonos Tzibur - communal offerings. The word "Machatzis' consists of 5 letters, the middle one being a "Tzadi", the first letter of the word ‘Tzdakah". Immediately flanking the Tzadi are a "Ches " and a "Yud", which spell the word "Chai" - life - and at the outer ends are the letters "Mem" and "Tof", which spells the word "Mais" - death. This is an allusion to the adage "Utzedakah Tatzil MiMaves" - Tzedakah saves from death.
Pinchas through his zealousness removed the plague from the Bnei Yisroel, thus committing an act of Tzedakah whereby life prevailed and death was excluded.
In the word "Chamosi" - "my anger" - it is the reverse. The middle letters are "Mem" and "Tof", which spells "Mais" - "death" - and the outer letters "Ches " and a "Yud", which spell the word "Chai" - life. Hashem was saying that Pinchas "Hayshiv Es Chamosi" - inverted the word "Chamosi " - chasing death away and bringing life.
http://revach.net/parshas-hashavua/quick-vort/Parshas-Pinchas-Vilna-Gaon-Pinchas-Turns-Around-The-Word-Chamosi/489