The latest episode of Arrow finally explains the purpose of Oliver's mission in season 8. All season long, Team Arrow has been gathering parts for a mysterious weapon, without knowing what it was or what the Monitor (LaMonica Garrett) planned to do with it. As it turns out, it had more to do with Lyla Michaels (Audrey Marie Anderson) than it did with Oliver Queen (Stephen Amell).

At the end of season 7 of Arrow, Oliver was told that the only way to save the multiverse from the coming Crisis was for him to sacrifice himself. Since the beginning of season 8, Oliver has been helping the Monitor prepare for the Crisis by traveling to places like Earth-2, Hong Kong, and Nanda Parbat to gather materials for a weapon. For a short while, Oliver doubted his mission and wondered if the Monitor was actually his enemy, but now Oliver is fully committed to completing his task for the Monitor and working with him to save the multiverse.

Related: Arrowverse Characters Who Died In The Crisis On Infinite Earths Comics

In Arrow season 8 episode 7, the mission reaches a conclusion when Team Arrow is sent back to where it all began: Lian Yu. After a long battle with old foes, Team Arrow is able to finish the weapon. William (Ben Lewis) discovers that the weapon can only be activated by someone with a specific DNA signature. This person is thought to be Oliver, but is revealed to be Lyla instead. After the weapon is used, Lyla leaves through a portal. She reappears in the episode's final scene in-costume as the Harbinger, and announces that the Crisis has begun.

Harbinger in Arrowverse New Costumes

The whole point of what Oliver has been doing throughout season 8 has been directly related to Lyla, who is apparently vital to their survival in the Crisis. As for what the Monitor intends for Lyla, the comics may provide the answer. In the comic book version of "Crisis on Infinite Earths", Harbinger is the one who the Monitor entrusts with gathering the forces necessary to oppose his nemesis, the Anti-Monitor.

Thanks to the Monitor, Harbinger had the power to create duplicates of herself, which she then sent to multiple Earths to recruit dozens of heroes and villains from multiple Earths. Since the Arrowverse's Harbinger has been seen recruiting characters like Batwoman (Ruby Rose), Flash (Grant Gustin), and the Legends in the "Crisis" teasers, it stands to reason that this could be what the Monitor's weapon did to Lyla. Lyla may be the person responsible for uniting the casts of all five Arrowverse shows for stopping the Crisis.

More: What To Expect From Arrow Season 8 When It Returns