is these chapter titles represent mc's thought?
It's the chant for the thunder spell Indignation from Tales of Phantasia. The full quote is:
"I stand in the place bathed in heavenly light. Thou art where the gate to the Underworld opens. Come forth, divine lightning! This is the end! Indignation!"
So besides being a reference to how blessed he is in this moment, it's also alluding to the fact that it's the storm that's allowing him to have this extremely sweet interaction. It's "divine lightning".
Really funny way to get that across though, and I have no idea if it's a localization call or what