Phinehas was a priest in the time of Moses. In his day Israel began to worship the false god Baal with the daughters of Moab. Their worship caused a plague to break out in the camp, so when Phinehas saw an Israelite man and a Moabite women enter a tent together – yada, yada, yada – he took a spear and killed them both. His zeal caused the plague to end (Cf. Num. 25).
In Jesus day the Pharisees were the arbiters of the law, and took their definition of being zealous for God from Phinehas; zeal for God was at the point of a knife. However, these religious leaders were actually just zealous hypocrites; judging others, but not themselves.
Jesus’ instruction about judging is clear – Don’t do it (Cf. Matt 7:1). Why shouldn’t we judge? Most people, including Christians, are very critical individuals. Therefore, judging causes us to come across as harsh, vindictive, and cruel leaving the one who judges with the idea that they are superior.
When it comes to judging remember this: Nothing in the spiritual realm is accomplished by judging someone else. Also, every wrong thing you find in another person is something that you’ll find in yourself, and is something that you accept in yourself. Lastly, there is always one fact that you do not know about another person, or about a situation.