You're chosen by the Lord. That alone makes you trustworthy.

Additionally, the casting requires some.... fortitude, and it sounds as if you've seen your share of battles.

This spell won't separate me from my vessel, just so you know. If you banish me, he comes too. It's something I'd prefer to keep secret because being banished is... excruciating. Additionally, I'm not even sure I can find my way back here if I'm sent away.