Looking at Luca while he dons that sinister smile, elder Gallus is forced to reevaluate his opinion of him.
He is a psychopath, a sadist who derives his pleasure from seeing another in pain.
With all the overwhelming power he has, he could have easily taken out Elder Gallus and the Arshbon. But he is not doing that, his nature wouldn't allow him to.
He wishes to see them in pain for as long as possible so that he can ascertain his dominance over them.
However!! That would be his eventual undoing.
The spirit of the Arshbon is tough. The more they are backed against a wall, the fiercer they will resist. And when they see that they have breached the limitation of their resistance, they will come to an understanding. Said understanding is what will make them surface stronger, emerge out of their cocoon so that they can grow stronger and resist the enemy's advancement even harder than before.