All Christians sin. All churches are blind to some of their sins. None of us is in a position to claim our theology is true because of the quality of our lives. Truth is grounded in God’s word, not our works.
While it is true that “you shall know them by their fruits” (Matthew 7:16), it is not true that you shall know their theology by their fruits. Man’s capacity for hypocrisy is great. And Jesus can say even of the Pharisees, “Practice and observe whatever they tell you—but not what they do” (Matthew 23:3).
And Paul says, concerning some heartless, pretentious evangelists, “Whether in pretense or in truth, Christ is proclaimed, and in that I rejoice” (Philippians 1:18). The fact that the devil makes himself an angel of light does not mean there is no such thing as an angel of light.
Ongoing, unrepented sin signals a false claim to faith. But the hypocrite may hold many true doctrines. In fact, that’s what hypocrisy means.
One generation is blind to some implications of their faith. Other generations are blind to others. One ethnic group is blind to one thing. Another ethnic group is blind to another.
My aim is not to whitewash the Reformed tradition. It is, with all other traditions, deeply tainted. My aim is to free you from needing to reject truth when spoken by sinners.