At the beginning of the parashah, Rashi writes,
תנחומא רבי במדרש נדרשת יפה זו פרשה.
Literally, this means, "The parashah of Korach is taught beautifully in the Midrash Tanchuma." But why does Rashi tell us where to look this up? It is unusual for Rashi to do this. The Pri Megadim (ה"ד ת"עה גומא תיבת קהלת) answers b’derech tzachus with the pasuk (Mishlei 15:23), טוב מה בעתו ודבר, "How good is a word in its time." It is ideal to speak words that are related to the times.
For example, if you are giving a drashah on Pesach, how good it is when you speak about matzah, the issur of chametz, the yom tov of Pesach, hilchos chol hamoed, and so on. Since you are discussing matters relevant to that specific time, it is proper, good, and beautiful. But if your drashah isn't about Pesach, you are not connected with the season and the happenings, which is generally a negative thing.
About this it states טוב מה בעתו דבר, how fortunate and how good it is when a person discusses matters that the listeners need to hear now and doesn’t give drashos about issues that the listeners of the moment have no significant need to hear.
Rashi writes, נדרשת יפה זו פרשה, which can be translated as, "It is always the right time to give a drashah about parashas Korach." Machlokes happen often, so it is always an appropriate time to discuss this topic of the severity of machlokes. If you give a drashah about machlokes, you are always speaking בעתו דבר, a word, at an appropriate time.
