What literary device is used in the following quote from Night: "the morning star shone in the sky. I too had become a different person."

Your best bet here is
. The morning star is often used to symbolize hope and guidance.
Elie realizes the transformation from night (symbolic of evil and spiritual darkness) into
something more beautiful with the emergence of the morning star. And he links himself to this
transformation, yet not in the way you'd expect. To understand this, it's important to read the
section that immediately follows this quote:

The student
of Talmud, the child I was, had been consumed by the flames. All that was left was a shape that
resembled me. My soul had been invaded €“ and devoured €“ by a black flame.

Elie has been transformed, too; however, he began as a child with
hope and now stands as a mere shadow of what he once was. The "black" flame of evil
and symbolic night has devoured him.

While the emergence of the morning star
is symbolic of a positive transformation, Elie's own transformation by comparison is
ironically the opposite: He has been drug from light into
darkness.