The Mishnah in Avos says הקנאה והתאוה והכבוד מוציאן את האדם מן העולם (ד כ"א), jealousy, lust and a desire for honor, remove a person from the world. Seforim explain that these three negative traits are the core, the basis of all other bad middos. All other bad character traits are an outgrowth of jealousy, lust, and a desire for honor.
Meforshim explain that by giving in to these ill desires, one loses both this world and the next. In this world, the obsession to satisfy these needs kills all potential for happiness and success. Consequently, one loses focus on fulfilling his mission as an Eved Hashem, and he loses his portion in the world to come. (עי' תפארת ישראל שם)
Meforshim cite examples of where each of these bad traits are displayed. The example brought for קנאה is Korach, the Mishnah here says that envy and its potential destruction were seen by Korach. (עי' תוס' יו"ט וחי' הגר"א שם)
Rabbeinu Yonah says that kinah can also refer to one's spiritual successes where one envies another's virtuous achievements in Torah and mitzvos. There is the concept of קנאת סופרים תרבה חכמה, envying the wise will increase wisdom. But with this too, he cautions it must be in a constructional manner; beneficial jealousy is one that drives action, it motivates one to become more diligent in his learning and increase his Avodas Hashem. Dangerous jealousy, however, is one that is only focused on what the other possesses and he does not, he only hopes that his friend would not attain that knowledge or quality. (רבינו יונה שם)
Therefore, one must seek to save himself from these harsh and destructive middos, for they only bring about bad, and envy completely ruins a person, as was seen by Korach.