This chapters explains so many things:-
1.It explains Zeref's and Mavis's powers to a certain extent.
2.It always felt Zeref wanted to die like Toguro from YYH (
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) this chapter provides us with that reason. Thus making END, when he first met Natsu he was sad as he wasn't powerful enough to kill him.
3.Mavis is "the black wizard" that's why Lumen Histoire was called darkness of FT by Ivan Dreyar.
4.It to an extent explains Zeref an Mavis's connection.
Still many mysteries like Zeria's or Natsu's background or disappearance of Lucy's mom remain but this chapter despite being 20 pages was great for explanations.