Not everyone was cut out to be a villain, just as not everyone was cut out to be a good person.
Whatever Quirrell had been like before, ever since he met Voldemort, he had basically had no chance of becoming a good person again.
But the Death Eaters were a den of villains, and he clearly wasn't suited to them either.
So Voldemort gave him the task of building a library.
It would make good use of his strengths while keeping him away from that den of villains. In Voldemort's view, it was a rather perfect solution.
"Luna."
After watching Quirrell leave, Voldemort turned to her and asked, "How have your lessons with Carlotta been going?"
"I'm not at the wand-making stage yet." Luna found a seat, sat down, and said dejectedly, "I have to learn a lot of things first. Teacher Carlotta said I'll need to study for at least half a year before we can talk about that."
"That means you have pretty good talent, Luna. Half a year of study usually isn't enough for a child, especially one as young as you."
Voldemort smiled as he came over and gave her nose a little pinch.
Of everyone he had met, Luna was the one he got along with best.
She wasn't afraid of him, and she didn't keep her distance. He didn't know if it was because of the Crown Horcrux.
Whatever the reason, Voldemort enjoyed her company.
But...
The child wasn't of much use to him, so he didn't pay her much attention.
"Neville, starting this afternoon, come here for an hour every day. I'll help you dissolve those mental thorns." Voldemort turned to Neville.
"All right, Teacher," Neville answered simply.
"Teacher, should I come along and study too?" Luna asked quickly.
Voldemort thought it over.