Some churches teach such a belief, even to the extent of making it a major doctrinal issue.
But others either remain neutral or teach that they indeed do mix and, on occasion, even must mix. But so much for what men say. Let's look instead at what the Bible says. A survey of the many reference materials available brings out many important points, as does the Bible itself. In the instances where such blunt indication is absent, there appears no indication that it could be otherwise.