Mendez has been deceived by the false prophet of the false god. The one true God calls man, not to slavery, but to communion with Him through His Son, Jesus Christ. By renouncing the redemptive salvation of Our Lord Jesus, Mendez condems himself to eternal slavery in the netherworld of the imposter.
In my religion we are all children of God; He has no grandchildren. I can find language that "the Lord is my shepherd" but this is taken metaphorically as a way of communicating that He is our provider.
The Jews struggled for a long time to be freed of slavery. I don't recall any references where they considered their bond to God to be a master and slave relationship.