Rav Kaminetsky explains that Yaakov had taught Yosef all that he’d learned in the Yeshiva (school) of Shem and Eiver where he studied, and where Yitzchok AND Avraham studied as well. The main strength of that school was that they taught Torah that could survive in negative environments. Avraham used it to deal with the rest of the world, Yitzchok used it to deal with Yishmael, and Yaakov used it to deal with Lavan and Esav. Now Yaakov was teaching it to Yosef, and the brothers were worried. Were they as bad as Esav or Lavan? Why would Yaakov have to teach Yosef that Torah? Little did they know that Yosef would need it to deal with Egypt, and all the trials he would face there. Yaakov loved Yosef more because he learned more, and WANTED the other brothers to be jealous (that’s why he made him the shirt), so that they’d want to learn it too! But instead they became jealous for the wrong reasons. It was THEN that Yosef tried to tell them that they shouldn’t be jealous, because he had to learn for his OWN sake, because he’d have to be a leader in a foreign land (as the dreams with stocks suggested, since there were no stalks where they lived). But the brothers had let themselves be blinded by hate, and couldn’t see the truth, as obvious as it may have been.
There’s an important lesson in all of this, and that is that jealousy can be used in a good way, as Yaakov TRIED to do. But if we’re not careful, we could miss the whole point, and end up doing things we shouldn’t. The first test is to ask ourselves if we want something because we need it, or simply because someone else has it. We should be jealous of things we can learn and grow from, like Torah knowledge, good character traits, and even courage and persistence. Everyone has qualities we can and SHOULD be jealous of, as long as we use it NOT to prove ourselves, but to improve ourselves.