The weekly Torah readings are known in Hebrew by their opening words. This week's reading, Ha'azinu, consists of the Song of Moses, beginning at Deuteronomy 32:1.
My portion shall descend like rain, my words shall distill as dew. (Deut. 32:2)
Zelig Pliskin, quoting Rabbi Bunim of Parshischo, explains the passage: "Words of admonition are analogous to rain. When rain falls on trees and plants, growth is not noticeable immediately. It takes time for the rain to have an effect. So too with admonition." (Love Your Neighbor, p. 432.)
It's true: if you try to change someone's mind about something, chances are they won't change their position right away. It's human nature that we don't like to be seen as easily swayed - and in general, that's a good thing. People like to feel they're making up their own minds. Moses was one of the greatest teachers in history; but as even a cursory reading of the Torah tells us, his "students" were not always the best learners!
All of us are "stiff-necked" at one time or another. Many of us have had our worldview radically altered over the last few years - and for most of us, this didn't happen overnight. The Torah is reminding us that even when our neighbors seem to be a bit "slow on the uptake", we should be patient with them and not give up.