Question

Why does the rain call itself eternal

Answer 1

It's related to water cycle as the line says that "I give back life to my origin" . We understand from it that Rain is the important thing for every living being . And as so water evaporates from rivers etc . which then form clouds and then comes down again in the form of rain and as we say it a water cycle it happens cyclically every time . So the origin in this is from where water evaporates and it came back there only again. Rain is eternal because the origin is the rivers etc. from which clouds forms and rain comes to its place again . And this continues so it will not die and is eternal.

Answer 2

because it is inside the earth