How does the authState property of the AngularFireAuth service work, and why should it be mapped?

Question

Angular

Greetings.
The authState property on the AngularFireAuth service returns an Observable object. authState should essentially return the state of the authentication. But why iterate over it with the map method? What does he keep in himself?
And I also can’t understand why take (1) is used in this case?
As far as I understand, take(1) returns the first value from the data passed to it.
But on the screen below I can not understand why.