Only God can help me understand what's going on now? I'm so lost

Turban is Seria's patron saint while moon guy is an evil banished God and he became the Lina's patron and made her a fake saintess with his evil power
Now they are both summoned into the world and probably going to fight idk
Turban is the guy inside the banner insignia Seria keeps seeing every time she pours her divine power into it, he looks like Rouche because he is who Seria loves the most, I don't understand the "biggest regret" part yet though