Guys this scene is important because our soft boi is thinking very hard.
He didn’t want to reveal one of his secrets. Being able to use magic freely, without an item, is very rare and not only that a commodity. So.. I guess in a way he didn’t want to be taken advantage of. Not that the chain would ever do something like that.
The life spell in particular takes a huge chunk of magic too, so after its cast he won’t be able to use any other spells; until its replenished. It’s also dark. It means he had many near death experiences to even know such a spell and perhaps the team could infer that. He knows they aren’t stupid.