Light - Rencal is generally considered a Lightbringer, who brought light into the newborn Illiadian universe in the form of Stars and the Illiadian sun when he conceived it, as well as a foil to Sh'ther Kei-Sihr, the Illiadian deity of Shadow. Many texts about Rencal speak of divine radiance.
Forge - Rencal's role as Illiad's main deity of creation also makes him the patron over the act of creating things through artistic and artisanal means. Most notably, Rencal's also known as the "Grand Sculptor" and, most notably by more desert- or mountain-dwelling Mikaru and Ree-Mai who tend to work with metals, as the "Great Artisan" or "The Worldsmith".
Peace - Ever since Illiad has started to make contact with other worlds, like Sancstoryl, so did Illiad's deities. Rencal is generally believed to make contracts with the deities of other worlds that allow people from other worlds protection on Illiad, while Illiadians meanwhile would be protected on other worlds. It's also notable that one of Rencal's first acts as a deity after creating the Illiadian universe was teaching the People of Illiad how to work together and live in peace with each other.
Life - As a deity of creation, Rencal is also a deity whose domain is the creation of Life, as he created all living creatures on Illiad himself.
Nature - Despite also being a deity of the Forge, closely associated with Civilization, Rencal is also a Nature-Deity simply due to the fact that he also created all of the Illiadian natural world. One of Rencal's biggest commandments is "The World around you is a gift to you. Treat it with respect and reverence." The main difference between Ree-Mai Tribal Rencalism and Mikaruian Reformed Rencalism is disagreements on how to do just that; Mikaru and Arrash generally build around nature or with respect to nature, while Ree-Mai tend to try to live as part of nature; though this is not a hard rule.
Order - As the Iron Emperor of the deities of Illiad, Rencal is tasked with keeping the Illiadian universe in order, so that everything works like how it's supposed to work. While comparatively hands-off for a deity, he does manage most of the things within The Marble Cathedral and tend to step in when Chaos and Despair reign supreme on Illiad.