Separation of Church & State ~ Fr. Ripperger

In my soul I feel convinced that Fr. Ripperger is speaking the truth here. But I have some serious questions. For example, is it possible for a ruler to conform to the Divine Positice Law without himself being Catholic? The answer would also help answer my other questions, because I have some impression that belief in Revelation is a gift of God which cannot be coerced nor induced by servile fear, for example by the servile fear of a State's decline..