For decades, Marvel Comics has toyed with the universe being destroyed or remade thanks to the Infinity Gems. Stories like Infinity Gauntlet and Secret Wars showed how these cosmic artifacts affect reality, so when the publisher decided to reconfigure them as the Infinity Stones (aligning with the Marvel Cinematic Universe), fans waited to see if their powers would be changed along with the name.
For the most part, they're basically the same, apart from their visual design. However, the Stones (Mind, Time, Power, Space, Soul and Reality) now operate in tandem with each other, like a circuit, which ideally enough forms an infinity sign. And in Infinity Wars #4, we find out which is the most powerful -- the Soul Stone.
Now, when they were the Infinity Gems, Marvel never really ranked them or labeled one as more powerful than the other. How powerful they were portrayed was based on what the users were trying to achieve with them. Of course, once an individual (like, say, Thanos) got their hands on all six, then that person could attain godlike powers. The Stones more or less follow this same pattern with Requiem (aka, Gamora turned evil) collecting them all, and using a special armor to reshape the universe, beginning by folding the universe in half.
But in this issue, as Requiem tries to harness the mysterious power of the God Quarry, we learn more that the Soul Stone actually holds the most power. The first hint comes from Loki, as he's trying to separate the mash-up of Wolverine and Emma Frost only to be attacked by Devondra, a spider that constantly tries to eat Requiem's enemies in an alternate reality. Loki reveals that from his time spent studying ancient Asgardian texts, he knows this is actually a soul-eating spider that creates universes from her silk.
We saw it trying to eat Hank Pym in Infinity Countdown #5, and Requiem has mentioned the creature several times before. Now, it's apparent the creature's feeding pattern is what allows the Soul World to exist. It's powered by Devondra feasting on souls within the reality created, and it's why inside the Soul Stone itself characters like Hank are being preyed upon. This is what allowed Gamora to merge people in Infinity Warps; she merely sewed several souls together to create a new reality.
Now, seeing as this Stone can allow a new reality to be built and can fuse souls together, one has to wonder if the Soul Gem was the driving force which allowed Thanos to snap half of the galaxy out of existence in Infinity Gauntlet. We believed it was a combination of all six, and driven by the Reality Stone, but another big moment in this issue lends credence to the theory that the Soul Stone should be feared the most.
At the God Quarry, Requiem tells Flowa (an Asgardian librarian documenting her journey) that once Devondra spins new threads within the Soul Stone, a new reality can be born. Basically, once the spider has eaten enough souls and is sated, the Stone enables its wielder to alter reality, or worse yet, remake it. Requiem has recognized this and is using the Stone as the driving force of her Infinity Armor. This power was actually stricken from the texts Loki read, confirming the Soul Stone is indeed the most powerful, so powerful the Asgardian elders considered it a taboo topic.
It's quite fitting, as Gamora still has a piece of her soul trapped within the artifact, so hopefully she figures out how to dislodge it soon. This might be the only way she realizes her crusade is that of a madwoman, and that instead of remaking reality, she might be on the verge of destroying not just her universe, but the multiverse as a whole.