The book's title is a direct quote from the apostle Paul's writing (Ep3v9) and refers to the fact that in terms of salvation history the current age is not as many believe "a fulfilment of Old Testament prophesies in a spiritualized form", but as a result of God's chosen nation's rejection of His purposes for them, effectively an unforetold epoch we know of as the Church age. In three of his epistles Paul affirms the nature of the current age to have been a divine secret, undisclosed through any Old Testament prophet and barely intimated by Jesus during His earthly ministry. The book explores the wondrous providential and dispensational implications of this mystery; and shows how such a perspective resolves numerous other tensions and mysteries within the Bible.