So, I’ll wager the guess that Savitar wants Barry to suffer seeing Iris’ death specifically so that he’ll make some radically bad decisions to go about saving her, which will inevitably include removing the Philosopher’s Stone from the Speed Force and allowing Savitar back into the world at large, where he can do more speedster-conquering.
And now I’ll wager a big hope that Iris actually will be mostly responsible for saving her own life somehow, making this less of a “damsel in distress” arc.
While speaking with TVLine, co-showrunner Aaron Helbing dodged a question about how Iris may play a part in preventing her own death, which is interesting in and of itself.