A new trailer for Eternals has finally been released , giving fans better looks at both the Deviants and Celestials. This also includes teases of the Eternals' incredible powers such as Ikaris' laser eyes and Sersi's ability to manipulate matter , as shown when she turned a crashing bus into flowers.
It even answered why the Eternals never interfered with humanity or attempted to help them in any way against global catastrophes like the one caused by Thanos. It was because the Celestials told them not to interfere with humanity unless it involved the Deviants.
Something else was mentioned in the trailer, which seems to be why the Eternals reunite again and could spell danger for humanity.
THE CONSEQUENCE OF THE INFINITY STONES
The newest trailer for Eternals provided a consequence of the Infinity Stones being used on Earth. As Ajak explains to Ikaris, the second use of them from Bruce Banner "provided the necessary energy for the Emergence to begin."
It isn't certain what "the Emergence" is, but considering all the global catastrophes seen happening in the trailer and looking to the comics, it might have something to do with the Earth's core and the Eternals' true purpose.
THE BIRTH OF A CELESTIAL
It was established in the comics during "Earth X" (1999) by Alex Ross and Jim Krueger, a series based in an alternate universe of the comics, that the Earth was implanted with a gestating Celestial egg. When hatched, it would emerge and destroy the planet.
This was mentioned again in the prime universe in "S.H.I.E.L.D." (2010) #4, being referred to as a common method for new Celestials to be born. Typically, it would take millions of years for the egg to hatch, but upon its emergence, it would consume the planet.
It could be that the use of the Infinity Stones on Earth hastened the growth of the Celestial egg, which triggers "the Emergence" that Ajak mentioned. In the trailer, viewers can see something actually falling to Earth, which could be the Celestial egg that was embedded into the planet.
It's possible that the goals of the Eternals will be to keep the Celestial egg dormant before it prematurely hatches and destroys the Earth and all of humanity. This is something that might already be starting in the trailer, as seen with the deformation of the land and sea.
Additionally, it was established in "Earth X" that one of the primary reasons Galactus existed was to consume planets specifically impregnated with Celestial eggs. Galactus ensured that the Celestials would not overpopulate the universe, which would end in its destruction.
It would certainly go a long way towards having Eternals connect with other future Marvel Studios projects featuring charaters like the X-Men and the Fantastic Four. Fans will find out the truth when Eternals comes to theaters on November 5, 2021.