Someone treats a right as a favor the powerful grant instead of a boundary they cannot cross.

The entire argument stands on this sentence, and it is doing two jobs at once. First, it moves rights out of the King's gift and into the order of things: they are not granted, so they cannot be revoked, only violated. Second, it makes the claim unfalsifiable by design — "self-evident" means it needs no proof and admits no debate, which is exactly what you need when you are about to commit treason and want the argument to hold before the shooting starts. Every later paragraph is downstream of this one: if rights are unalienable, government exists only to secure them, and a government that destroys them has no claim on obedience.