@Yamibi According to 3rd party spoilers,
the holy sword is rejecting Claude because the ruins trip awakened the demon power inside him, and said power clashes with the holy power.
Claude has demon power due to 1st timeline events - he also fell in love with Ivona then, but she died before he could get the temple to cure her. The temple priests convinced Claude to eat the heart of the demon lord, where he used its power to turn back time for Ivona.
Apparently the temple wanted to turn Claude into a new demon lord, to serve as a antagonist to rally their believers against so they can keep maintaining religious power.