Numbers 21:8 - Numbers 32:19
"And Israel joined himself unto Baalpeor: and the anger of the Lord was kindled against Israel." Numbers 25:3
The people were openly committing sin. There was no shame for their actions and they did not care who knew what they were doing. God's anger was kindled toward them.
When Phinehas sees a man bring his Midianish lover toward the temple he responded. His actions stopped God's wrath toward the people of Israel.
"Phinehas, the son of Eleazar, the son of Aaron the priest, hath turned my wrath away from the children of Israel, while he was zealous for my sake among them, that I consumed not the children of Israel in my jealousy.
Wherefore say, Behold, I give unto him my covenant of peace:
And he shall have it, and his seed after him, even the covenant of an everlasting priesthood; because he was zealous for his God, and made an atonement for the children of Israel." Numbers 25:11-13
God blessed Phinehas's life and lineage with peace.
I want to be zealous for my God. It will come with a price. I may be alone. As with Phineas, who did not stand by and just watch things happen, he was blessed by God for his actions towards sin.