by Rabbi Avigdor Miller
At the beginning of the Torah, the first mother when she had the very first child that was ever born, she gave it a name and that name is extremely significant. We have to pay so much attention to that name because it’s the key to everything else that we do in this world. “She called his name Kayin, and she said konissi ish es Hashem — I acquired a man with Hashem”...
Konein means to acquire, but kinei means to be jealous. What’s jealous got to do with acquiring? Konein means I want to take something; kinei means I’m not interested in taking, I want [him not to have it]. That’s the difference.
When you see someone doing something good, be jealous of him
So Kayin should have been a koi’ein. Instead he became a mukanei, he became jealous. When Kayin brought that korbon to Hashem, and then Hevel came and also brought a korbon, he followed his brother’s example. His brother was the first one of the brothers to bring a korbon. So Hevel followed his brother’s example. But Hevel brought a better korbon. He showed more gratitude and devotion to Hashem.
So “vayisa Hashem el Hevel vu’el minchoso — Hashem turned to Hevel.” He showed a certain manifestation that He favored Hevel’s offering more, and that burnt Kayin up.“Vayichar lukayin mu’od — He became very much upset.” He could have reacted in a different way, he could have thought if Hakodosh Boruch Hu favored Hevel because he brought a better korbon, next time I will outdo his korbon. I’ll bring a still better korbon. But instead he concentrated on his hostility, animosity, his hatred towards his brother because his brother gained the favor of Hashem this time.
Now Kayin did not invent the quality of kinoh. He didn’t invent jealousy. Hakodosh Boruch Hu invented jealousy, it is put into human nature. So the question arises, does Hakodosh Boruch Hu give a person negative qualities? “Ho’elokim osso es ho’odom yoshor” it states, Elokim made man right...
The quality of jealousy is one of the most useful and precious gifts that Hashem ever gave us. We have to be jealous. That’s what Chava meant: she wanted him to be jealous and try to get as much as he can of good qualities in this world. When you see someone doing something good, be jealous of him and say I want to do it myself. That’s what she said to her son Kayin: be a koinen, acquire as much as you can in this world.
The quality of jealousy is one of the most useful and precious gifts that Hashem ever gave us. We have to be jealous. — Legacy of Chava (#834)