He controlled the forcefield around the city, and has access to a transporter that can move people across the galaxy.
If Banjoman wanted to convince some shepherdess the he was god and that she had the chosen on in her belly that he put there with his sporocystian dong, it wouldn't have been a hard sell.
Do you think that Mary was the first woman who God approached?
She was way down on the list.
First any one smart enough to realize that God is a dodgy bastard would have told him to fuck off, because they're obviously doomed players cast in a metaphor to help future generations work out their problems, so fuck that, the future are a bunch of assholes that can fuck themselves, meanwhile all the other husbands figured out that their wives were cheating on them, and bashed their wive's in the head with a rock.
God had to look for idiots that couldn't anticipate how he was plotting their downfall and then curse his sudden but enevitable betrayal before he got his ducks in a row, so basically finding the perfect mark was quite difficult.
