In this week's Parsha, the Torah tells us one of the Ten Commandments is "Do not murder." However, one would think that it seems pretty obvious that it's cruel to murder. It's is a human being; someone's father, someone's husband, someone's child. The Rambam, in Hilchot Rotzeach, Perek Daled, teaches us that murder is wrong and worse than other sins in the Torah that require the death penalty (Adultery, Chillul Shabbat, Avodah Zarah). The Rambam says that although many of these sins can be considered more severe than murder, they don't destroy the establishment of the world. While the other sins are between man and God, killing is between man and man. Anyone who murders is a complete Rasha, and any of the merits that he may have achieved prior will not save him from the penalty of this sin.
The other sins that deserve the death penalty require the full Halachot of testimony to carry out the death penalty. For example, we need two witnesses who saw the murder simultaneously. Let's say one person is looking out the window and sees someone doing Avoda Zara. He moves away and calls his friend to see (since they did not see it simultaneously together) there will be no death penalty. However, in the case of murder, if for whatever reason the testimony requirements are not met, like the above example, Beit Din will not directly kill him but bring about his death in a different way (see the Rambam).
The Sefer Hachinuch (Mitzvah 1 and Mitzvah 34) says that it's known, to all those who live under the sun, that G-d created the world and commanded us to be fruitful and multiple to establish His world. It is His will that the world will become established, and this is the first mitzvah in the Torah. He gives us an internal appreciation for life so that we don't come to destroy the world and humanity. However, this Chinuch continues that there are wicked people, slanders, and wanton sinners who are not from those who establish the world and about them.
In Mishlei Perek 11, Shlomo Hamelech says that when those people perish, we rejoice since they do not build the world but destroy it with all their might. Chazal taught us that it's like removing thorns from a vineyard: now the fruit can multiple and improve. Remember that in Shemoneh Esrei, we also daven for these wicked people to die. As we said previously, the first mitzvah God commanded man was to be fruitful and multiple to establish the world. From the Rambam and Sefer Hachinuch, we learn that the gravity of sin gets measured by its effect on the established world.
We see in the Sefer Hachinuch that it's not only murderers that destroy the world but wonton on sinners and slanders. So much so that we rejoice in their demise.
If we're supposed to celebrate when those sinners get destroyed, how much more do we have to appreciate and praise those that fix, establish, & build the world? To stay away from the negative and destructive forces surrounding us and attach ourselves to those focused on bettering the world. To be a person focused on establishing and building the world.