"I am an angel," he says, frowning, "and you lack faith. If my Father was before you, would you question Him, too?"

Maybe it's not a fair comparison-- his Father never came to Earth without announcing Himself with great power and splendor, since apparently subtlety hadn't been invented yet-- but He'd also be terribly displeased that one of His creations denied one of His angels. Especially Samael, because he's the favorite and he knows it.