Key piece of the last war
[I'm assuming 'last war' because the upcoming war between Iran and Israel will so devastate Iran, that Iran would then not be able to participate in the Gog and Magog invasion for decades. And I just don't see God kicking the proverbial can of the end of this age, up the road that far into the future. "The END" is closer than that based on Matthew 24 and the modern-day miracle of prosperous Israel.]

If Israel instigates the war with Persia, they would do so before the S-300 is delivered. The S-300 delivery delay is probably something Netanyahu personally requested on his past weekend trip to visit Putin.

Russia: S-300 delivery delayed
The Interfax news agency on Wednesday cited a top Russian defense official as saying that S-300 air defense missiles will be delivered to Iran once unspecified technical problems are resolved.