Warning! Spoilers for Venom #25 below!
The Avengers have battled the biggest threats in the galaxy. They've fought everyone from Galactus, to Thanos, to the Dark Phoenix, to Annihilus, and come out victorious on more occasions than they haven't. However, their next threat might be their deadliest yet, as they just learned about Knull, the God of the Symbiotes.
Knull first appeared in Venom #3 by Donny Cates and Ryan Stegman. Knull is an ancient being who is responsible for creating symbiotes as a weapon for his own control - as Carnage is his servant. The villain' created the god-killing Necrosword and intends on enveloping the entire universe. With Knull (and his symbiote dragons) coming to Earth, Eddie Brock finally filled in the Avengers on the pending cosmic threat.
Venom #25 by Cates and Mark Bagley sees Brock in a confessional of sorts, where it's revealed he's actually filling in the Avengers on what he's been through with Knull, Carnage, and the symbiotes. Brock says "I need to tell you about Knull," which gets an "Odin's beard," response out of Thor since he went against a nameless Knull in Jason Aaron's Thor: God of Thunder series. Captain America asks what exactly Knull is, and Brock responds by telling him "It's bad cap." Brock explains that while Knull is the biggest threat, he feels other vibrations in the air of other symbiote-related villains coming as well. "I don't know if we'll survive in one piece... if we survive at all..." Brock warns the superteam.
It's about time Eddie filled in the Avengers on Knull and other potential symbiote-related villains to Earth. Taking on such a powerful force would be impossible by himself, even if he feels somewhat responsible. The Avengers might not be able to take him down quickly, but having Earth's Mightiest Heroes around ahead of Knull's arrival will certainly give Eddie a better chance at winning their upcoming battle.
Eddie Brock has been through a lot, so finally asking for a helping hand is the right move. Knull has universe-destroying power potential. Now, Eddie won't have to face that alone. Teaming-up with the Avengers might be a last resort move for him, but the upcoming battle is so much bigger than Venom. It's a matter of life or death for the entire planet. Cates and Stegman (with an assist from Bagley) have built an incredible, massive story for Eddie Brock - now it's time for him (and the Avengers) to face the music.