Eren made the effort to make Roza realize his perspective.
He did this so he could gain her trust seamlessly.
After all, he could eradicate Vepar or make the demon leave Roza's body using the unchangeable writ he had as the true inheritor of the Elder Ichor bloodline and successor to Aleph's divine throne.
But he couldn't control her actions. Not really. Not yet.
Vepar was loyal to Eren but that loyalty was driven by the instinctual fear of someone who could harm her despite her seemingly immortal status. Roza was also like that by extension. All her actions indicated that she was fearful of Eren and what he could do to her.
The stuttering. The shaky voice. The jittery nerves. The constant act of worrying. And the need to please him so that he doesn't do anything to her. Roza was a complete contrast to Vepar's previous demonic possession which was Reva Rain.
