Phinehas, Son of Eleazar, Slays the Chieftain and The Woman (Numbers 25:7-8 a).
‘And when Phinehas, the son of Eleazar, the son of Aaron the priest, saw it, he rose up from the midst of the congregation, and took a spear in his hand, and he went after the man of Israel into the inner portion of the tent, and thrust both of them through, the man of Israel, and the woman through her body.'
Phinehas, the son of the High Priest Eleazar, was appalled at this behaviour, and constrained at the plague which had broken out. He rightly saw the man's behaviour as an insult against Yahweh and as bringing shame on Yahweh's name, and as defiling the camp. And leaving the gathered throng he seized a spear, and followed them into their tent, and thrust the spear, first through the man and then the woman. Someone who saw it remembered that it was through her stomach. That was where her childbearing would become apparent, and he made the punishment fit the crime
In acting like this Phinehas would see himself as fulfilling his priestly duty, for the penalty for idolatry was instant death. He was acting as public executioner against an open sin (see Deuteronomy 13:9), but because the plague had broken out he had recognised the need for fast action. He was also in principle carrying out Yahweh's command in Numbers 25:4, for those who were hung out in the sun would have to be slain before they were hung out.
His action was actually very similar to that commanded by Moses at the incident of the molten calf at Sinai when he had commanded the responding Levites to slay those who had sinned (Exodus 32:27). Indeed he may well have remembered that and been determined to demonstrate that he was on Yahweh's side.
As A Result of His Action Judgment By Plague Is Stayed (Numbers 25:8 b).
‘So the plague was stayed from the children of Israel.'
We are now told that in fact a plague, previously unmentioned, had broken out in the camp. But as a result of the decisive action of Phinehas the plague was now stayed, and its effect began to die down