Unknown to men, but known to God.
(God Willed it to remain “hidden” as His “Mystery” or “Secret” for His Highest Glory when All is Revealed One Day).
The famous Dietelmaier has this to say: “Universalism in the fourth century drove its roots down deeply, alike in the East and West, and had very many defenders.”
Roots run deep and is mostly hidden (you can’t see it from the surface).
As the Word of God declares this Truth:
so that what was spoken through the prophet might be fulfilled: “I will open My mouth in parables; I will declare things kept secret from the foundation of the world.” – God speaks in (Matthew 13:35)