mystery, mysteries, hidden truth, hidden truths

Definition:

In the Bible, the term "mystery" refers to something unknown or difficult to understand that God is now explaining.

The New Testament states that the gospel of Christ was a mystery that was not known in past ages.
One of the specific points described as a mystery is that Jews and Gentiles would be equal in Christ.
This term could also be translated as "secret" or "hidden things" or "something unknown."