The Jewish people were given very specific instructions about their conquest of Eretz Yisroel. The Torah commands us: When you enter the land destroy all places where the previous occupants worshiped their gods. Check thoroughly on the high mountains and hills and under every leafy tree. Break apart their altars, smash their monuments and burn their sacred trees. Remove their graven images and uproot every trace of idol worship from the land. Do not do the same thing to Hashem your G-d. 

 This is very odd. The Torah tells us to be Hashem’s zealots destroying every trace of idol worship that might dishonor Hashem and in the same breath tell us “Do not do the same to Hashem your G-d”! 

 Indeed, the Talmud learns from here that it is forbidden to erase G-d’s name or destroy any part of the Beis Hamikdosh. We are also reminded not to act in a way that will bring about the destruction of the Beis Hamikdosh. 

 Are we talking to the same people here? How could people who have fought the war of Hasem even consider demolishing the Beis Hamikdosh? 

 Reb Shach makes the following point: Jews are by nature merciful. However, If somebody acts in a violent fashion – even if it is for a good reason – they will inevitably be affected adversely. Violence breeds violence, and after accustoming themselves to violence destroying the pagan idols, it is quite possible that the Jewish people could turn around and to the very same thing to those who are close to them 

 Golda Meir, the prime minister of Israel, is quote das saying “”I can forgive you for murdering our sons, but I cannot forgive you for making our sons murderers.”

 We find a similar concept later in the parsha: The Torah tells us that if a city becomes completely evil, with no outside help, that city must be destroyed. The Torah outlines the blanket executions and the destruction of the city to a pile of rubble and ends with a blessing : G-d will give you mercy and you will be merciful. 

Although this entire law is theoretical, and according to many did not happen ever in history, the Torah is teaching us a lesson: 

If we are violent , no matter the reason, we will need extra help in the future becoming merciful. 

 Every action we do has an effect on our personality. We may not become carried away with ourselves. 

 Reb Aharon Kotler takes this a step further, perhaps arguing with Reb Shach. He writes that this lack of mercy is a result of our lack of mercy going in. If we would have the proper intentions going in the results would not be damaging to our personalities. 

No matter how righteous we are, we need to be cognizant the effect of our actions on our souls.