Under Roman’s Castle, hidden inside the center of the hyper dodecahedron, are the Master Runes. Using the original runes of that universe, Roman, Death, and Magnus created this set that spelled out what could be done with magic by mortals. They even shaped the natures of divine domains and the nature of wild magic. As runes lost to time are recovered and their meanings translated, the master set got rewritten for more precise meanings and confining of magic.
Consider runes akin to carts. They facilitate the use of magic, yet also put on constraints to prevent more people from rising to godhood than already have. When casters cast magic, the somatic and verbal components themselves form part of these runes. Think of these as making the ability to cast more efficient. A power caster would not need to use runes, but do so at great waste of power. Though the average spell caster might never reach such reaches of power, sorcerers can briefly touch these heights from time to time.