Conversation so far:
What is meant by secular nature?
By the time of Horace Mann's leadership in education, various developments fostered a secular school system with a religiously passive stance.
What are some important aspects of secular nature?
Horace Mann stated that this position resulted in a near-universal use of the Bible in the schools of Massachusetts.
Was Horace Mann well known to a lot of people?
Horace Mann worked with a remarkable intensity, holding teachers' conventions, delivering numerous lectures and addresses, carrying on an extensive correspondence, and introducing numerous reforms.
What else did Horace Mann do regarding the secular nature?
Horace Mann stated that this position resulted in a near-universal use of the Bible in the schools of Massachusetts.

Question: Was there any controversy involving what he stated?
Self-contained rewrite: Was there any controversy involving what Horace Mann stated about the use of the Bible in Massachusetts schools?