We don’t learn to hear.
The only thing that we can really learn is that something may happen, and when it comes, to listen.
In the first revelation to Moses, he is not sure what has happened; he has to be given some kind of sign.
There’s an immediate call to see a sign, the burning bush, just in order to come close, which is again the same thing: it’s like knocking on the door, like feeling a hand on your shoulder.
It’s not in itself a message, but it is a kind of awakening.
Moses hears it.
The Midrash says that later, Moses says to God, “Reveal Yourself to me.”
And God says, “You cannot see My face. I will cover you and you will see something anyway.”
And the Midrash says that God told Moses: “When I wanted it, you didn’t want it. You hid your face. When you want, I don’t want it.”
Sometimes the only thing to be learned is this: when the call comes, jump!
–Rabbi Adin Steinsaltz