The Whispers in Final Fantasy 7 Remake have a somewhat mysterious motive in the game. Sometimes they seem to hinder the protagonists, while other times they appear to help them achieve their goals. According to Red XIII, they are the "arbiters of fate" who make sure destiny happens as intended, which explains a majority of their actions. Yet even with this knowledge, some of their gestures in FF7R don't fully follow this logic.
[Warning: SPOILERS for Final Fantasy 7 & Final Fantasy 7 Remake Below]
Obvious instances of the Whispers maintaining the original FF7's timeline include when Avalanche decides not to take Cloud on their Reactor 5 mission. The Whispers injure Jessie so Cloud has to go. In the Sector 5 church, they prevent Cloud from killing Reno, and they whisk Hojo away in his lab when he almost reveals Cloud's true identity. Yet, a major conundrum with the Whispers is near the end of the game when they appear to be helping Sephiroth in the form of Whisper Viridi, Whisper Croceo, Whisper Rubrum, and the Whisper Harbinger. By this point it's clear Sephiroth is drastically changing the narrative, so why are they aiding him?
One well-researched theorist, YouTuber Whispers represent FF7's Lifestream, or the souls that make it up. He suggests that some of the Whispers - especially the aforementioned ones - have been corrupted by Sephiroth's presence within the Lifestream and are doing his bidding similar to the numbered tattooed clones that Sephiroth controls in FF7 Remake. This would explain why their actions don't always seem to be preserving destiny as previously described.
Final Fantasy 7 Remake: The Whispers & The Negative Lifestream
In the original FF7, Cloud discovers Professor Gast's videos with Aerith's birthmother, Ifalna, at Icicle Inn. Here it's explained when Jenova fell from the sky 2000 years ago, she spread a virus that sounds awfully similar to the Geostigma disease in the Final Fantasy 7: Advent Children film, which takes place two years after Meteorfall. When Sephiroth is defeated at the end of the original FF7, he falls into the Lifestream, corrupting parts of it. Geostigma is a result of that corruption, or "negative Lifestream," that infects humans who seem to have given up hope or the will to live in Final Fantasy: Advent Children.
It's unclear if the Sephiroth in FF7 Remake is from a post-Advent Children timeline. Yet even if he's not, he still fell in the Lifestream prior to FF7 and FF7 Remake's events, and Jenova's previous virus 2000 years ago also befouled parts of the Lifestream. It's the Jenova cells injected into the hooded and tattooed Sephiroth clones that eventually allows him to control them, and a similar scenario seems to be happening with some of the Whispers. Sleepezi draws attention to the purple ones, like the Enigmatic Spectre and the Whisper Harbinger, which seem to specifically be linked to Sephiroth. Additionally, the Whispers Viridi, Croceo, and Rubrum have been confirmed to mimic the fighting style of Sephiroth's remnants Loz, Yazoo, and Kadaj from Advent Children, who are physical manifestations of Sephiroth's will.
Although there is still much left for speculation, this notion of the Whispers representing souls within the Lifestream - with some of them being tainted by Sephiroth - does provide a good explanation as to why they assist his destiny-defying actions near FF7 Remake's finale and while other times they act in accordance with Red XIII's explanation. Hopefully all this and more will be clarified with the next installment of Final Fantasy 7 Remake.
Source: Sleepezi/YouTube
