The quoted text comes from chapter 4 of Neil Gaiman's Coraline, taken from a conversation between Coraline and the cat.
Identity is one of Coraline's driving themes. As the book begins, Coraline is characterized as a young girl feeling adrift and misunderstood in the world she inhabits. Her parents seem to have little time for her, and her neighbors can't even get her name right (no matter how many times she tries to correct them).
The beldam attempts to take advantage of Coraline's fundamental dissatisfaction, as she creates a false world that would appeal to Coraline herself. But the fact remains: regardless of Coraline's own frustrations with her life, that world is genuinely real (as are the people within it), whereas the beldam (even notwithstanding her fundamental malice) can only offer imitations.
Thus, the cat's words point towards key themes that are woven across the book: Coraline is a story about Coraline finding out who she is, while opposing the nightmarish beldam. In this, she comes to understand qualities about herself that she had never previously known she possessed, perhaps most notably her bravery and resourcefulness. The cat, being defined by its instincts and feline nature, knows precisely what it is. Coraline, on the other hand, first needs to complete her trial by fire before she can begin to do the same.