'Mystery' in the Bible

He made known to us the mystery of His will according to His good pleasure, which He purposed in Christ,

and that by [divine] revelation the mystery was made known to me, as I have already written in brief.

By referring to this, when you read it you can understand my insight into the mystery of Christ,

which in other generations was not disclosed to mankind, as it has now been revealed to His holy apostles and prophets by the [Holy] Spirit;

and to make plain [to everyone] the plan of the mystery [regarding the uniting of believing Jews and Gentiles into one body] which [until now] was kept hidden through the ages in [the mind of] God who created all things.

This mystery [of two becoming one] is great; but I am speaking with reference to [the relationship of] Christ and the church.

And pray for me, that words may be given to me when I open my mouth, to proclaim boldly the mystery of the good news [of salvation],