"The term mysteries of God as used in the Book of Mormon denotes the saving principles of the gospel of Jesus Christ. They are termed mysteries because they are unavailable to the natural man, not because they are mysterious or difficult to understand. They must be revealed from God through faith and obedience. They are designed to lead God's children to eternal life.
"'A mystery is a truth that cannot be known except through divine revelation—a sacred secret. In the days of Paul the important truth that Gentiles were to be admitted to the Kingdom of God without observing the Law of Moses was a 'mystery' (Eph. 1:9-11; Col. 1:25-27). In our day such great truths as those pertaining to the restoration of the Priesthood, the work for the dead, and the re-establishment of the Church are 'mysteries,' because they could not have been discovered except by revelation.' (Hyrum M. Smith and Janne M. Sjodahl, The Doctrine and Covenants Commentary, p. 141)
"It was their knowledge of the mysteries of God that qualified Nephi to write his record and King Benjamin to preach his sermon. The material between Mosiah 2:9 and 5:15 constitutes a discussion of some of the most important mysteries of God." (Book of Mormon Student Manual, 1981, p. 154)
Neal A. Maxwell
"As we see from the content of Benjamin's sermon, the so-called mysteries referred to by King Benjamin are actually the plain but precious things required for salvation and for exaltation: (quotes Mosiah 1:5)." (John W. Welch, and Stephen D. Ricks, King Benjamin's Speech: Made Simple, p. 6)