The Space Guild represents, along with the Order of mentat and Bene Gesserit Sisterhood, one of the three pillars that acts with and against the Empire, keeping its aims at bay and balancing its powers. With the release of the Dune film, why not take the opportunity to talk about it? Frank Herbert's work has inspired other great franchises, one of them all Star Wars, and their modernity even after some time still makes them noteworthy today. The parts full of spoilers for those unfamiliar with the saga will be marked as such and absolutely avoidable.
The Space Guild emerged at the end of the Butlerian Jihad to respond to a need, just like Bene Gesserit and Mentat: to find a way to do what the sentient machines offered without breaking the new dictates. Specifically, the Space Guild deals with transport and holds a monopoly in the known universe, pushing anyone who needs to move goods or people to get on one of their transatlantic liners. Through the use of the Navigators, beings who have transcended the human form, the Space Guild is able to offer travel at the speed of light, allowing the movement between different and very distant systems.
It is not well known how this monopoly came into existence, probably the control over the Navigators has allowed the Space Guild to establish itself over time as the best solution for large displacements.
The Navigators of the Space Guild
The hierarchical structure has always remained a secret, unlike the Bene Gesserit Sisterhood, but many are known to have joined it in hopes of becoming Navigators.
Navigators are almost mythological beings. These are human beings subjected to the exposure of incredible quantities of spice to the point of forcibly evolving, changing themselves to become something that no longer resembles a man. Navigators can boast of conditioning and training to be able to navigate among the stars at speeds higher than those of light, making use of a particular form of foreknowledge due to spice.
Given the indissoluble link with the substance extracted on the planet arrakis, the Space Guild offers its side to anyone who boasts a monopoly on the spice or threatens to cut off their supplies. After all, if a normal person were deprived of the cinnamon-smelling substance, they would die, the Space Guild would lose all of its monopoly.