Unfortunately, this reponse doesn't address the issue. If your god has a plan for your life that includes suffering, that does not constrain the actions of someone who might free you of suffering by way of a mercy killing. Similarily a test to YOUR faith does not limit the actions of another. And the fact that murder is immoral means committing it for the sake of someone else's soul is the ultimate sacrifice. That self-sacrifice is the central tenet of Christianity with respect to Jesus.