The gospel itself is a mystery, which is why it requires a prior work of God for sinners to understand it.here is just one example:Colossians 1:25-27 KJV(25) Whereof I am made a minister, according to the dispensation of God which is given to me for you, to fulfil the word of God;(26) Even the mystery which hath been hid from ages and from generations, but now is made manifest to his saints:(27)