Invocation

Invocation is a powerful but difficult form of magic. Invokers use the Sigils, the primordial language woven into Koru through the Obelisks, to directly manipulate Ur, thereby reshaping reality. It was this power which allowed the Korsamu to ascend to godhood.
Despite millennia of study, the Sigils are not well understood and the Primordial language of their use even less so. Those who would unlock their power must form a sentence in Primordial expressing their goal. If they form and utter the sentence correctly and their will is strong enough, the world will reshape to match their invocation. Any mistake in pronunciation, vocabulary, or syntax causes the spell to fail, or worse, to come out wrong, often with disastrous consequences.
Invoking the power of the Sigils is demanding and often leaves the invoker physically and mentally exhausted, even after a successful invocation. A failed invocation, in addition to potentially unleashing undesired changes upon the world, can rack the invoker's mind eroding their sanity. Those unfamiliar with the Sigils cannot understand the words spoken during an invocation.
Mortals' limited understanding of Primordial heavily restricts what changes they can effect with the Sigils. This range is further restricted by the common preference for using rote invocations: spells that have been memorized and repeatedly practiced. This greatly improves the accuracy of the invoker's invocations and reduces the chance of magical mishap.
The Hambru'u generally hid the art from mortals, keeping its power for themselves. As a result, it did not become commonplace until after the Kataroth. The Empire of Eleyha made heavy use of invocation, but since its fall, the art has become considerably less common.