While Berserk's Golden Age arc had some of the most explosive and iconic moments in manga, one chapter was basically erased from future publication because of its shocking content, to the point that the creator regretted making it. Fortunately, it is readily available online, and while it is best to wait for the manga to reveal it all eventually, the chapter is still great and makes sense of many things.

Berserk chapter #83, titled God of the Abyss (2), was released on July 12, 1996, in Young Animal issue #14. However, when volume #13 was compiled and released, the chapter was omitted from the volume at the request of the creator, Kentaro Miura. The real reason for this wasn't revealed until years later in 2009 when Miura said he did this because of how the events and revelations in chapter #83 would limit the ideas and potential story developments. Furthermore, he also said that he did not know if the Idea of Evil would ever appear in the manga again or not. Until the manga revisits this development or not, it should be safe to conclude that God is canon in Berserk.

God Was Temporarily Confirmed to Exist in Berserk

This Revelation Came Too Early According to Miura

Chapter #83 focused on Griffith, on the verge of his ascension to the God Hand, who was sinking and being confronted with the lives of the Band of Hawks that he had just sacrificed. Once he reached the bottom, he saw an entity that introduced itself as the Idea of Evil. Shaped like a heart that breathes out a swirling gas, the Idea reveals that the collective consciousness of humanity gave birth to it to make sense of all the sadness, suffering, and death that inflicted them.

In essence, humans created their God. Furthermore, the Idea told Griffith that it creates destiny for every man, and weaved the threads of fate to birth Griffith and make him who he is so that he will either bring about salvation or great destruction to humanity.

It's because I wanted Berserk's world to be revealed just that far, not any more than that. The appearance of God in the manga conclusively determines its range. I thought that might limit the freedom of the story development. I myself don't know if the Idea of Evil will show up again in the manga or not.

- Kentaro Miura, 2009.

For something as huge as revealing a God in the series, it makes sense why Miura asked for the chapter not to be published in the volumes. It would heavily limit a lot of the developments that happened later and remove the charm of a lot of interesting plot points.

For example, readers not knowing that a God exists in the series makes the character of Father Mozgus and his cult-like devotion to a higher being much more interesting. While the Idea of Evil is certainly a great addition to the series worldbuilding, it would be best to leave it for much later in the series, and revealing it in the second story arc seemed a bit too hasty.

Berserk Could See the Introduction of God Again

Miura's Successor Could Pick Up That Thread

The Idea of Evil would surely explain a lot of lingering mysteries in the series, such as the true nature of the apostles and the role of the God Hand, who are revealed as the executors of the Idea of Evil's will in the erased chapter. While it was too early to introduce the idea of evil, this concept could make its return to Berserk sooner or later if Kentaro Miura decided to stick with it and told his successor, Kouji Mori, about it. If the series does end up revisiting this, the possible plot developments would be extremely exciting and could even signify the nearing of the series' end.

Source: Translated interview by Reddit u/GentlemanGhost1.