When Barry asks Savitar why they're enemies, he replies through Julian, "Because we had to be, Only one of us could live." This closely resembles the prophecy from Harry Potter and the Order of the Phoenix: "Either must die at the hand of the other, for neither can live while the other survives."
Julian refers to himself as Judas when he talks about the one that could possibly betray the team. Judas Iscariot was the one that betrayed Jesus Christ to the Romans. Tom Felton had a role in the movie Risen that was centered around the story of Jesus Christ after his crucifixion.
This was the first episode where Savitar's appearance was not CGI.
When Wally was hallucinating Savitar to which the hallucination of Savitar becomes Barry as the Flash, it foreshadows his identity into being the evil future version of Barry to which his identity has been revealed in the episode "I Know Who You Are".