Before sin entered the world and disconnected human nature from perfect union with God, our first parents were able to ‘see’ God through faith, by the unimpeded sanctifying grace that was offered (but rejected).

This spiritual sight is restored by the grace won for humanity on the cross, albeit as a bit more cloudy and indistinct due to the continued brokenness of our nature.

Hence, to explain the truth and beauty of the Nicene Creed and moral doctrine to people who reject this gift of second opportunity, is like trying to explain colors of the rainbow to people who have been born blind.

Yes, right reason without faith can theoretically see the truth of natural law morality and natural theology. However, in a post-Christian world, when Heaven’s second-chance Gift has been squandered in favor of selfishness, it’s virtually impossible to see these truths without faith.

Analogies:

Faith = spiritual sight; Reason = natural eyesight; Sin = cloudiness; Post-Christian culture = darkness; Grace = spiritual flashlight.

God is light (Jn 8:12; 1 Jn 1:5). His gift of grace is His divine Life within us. Those who accept are able to see. Those who reject remain blind.