What does Paul mean by 'mystery'?
Paul's 'mystery' refers to a secret hidden in God from the beginning of the world, or the ages, and not revealed through the Old Testament. It is the fellowship of the mystery: God now going to Gentiles with the Gospel of the Grace of God through Jesus Christ.
Les explains that Paul's use of 'mystery' means a secret, kept hidden in God, the same God who created all things by Jesus Christ. It had been kept secret all the way up through the Old Testament; not a word was said about God going to Gentiles with the Gospel of the Grace of God. Paul's apostleship was to make all men see this fellowship of the mystery, and in Galatians 3:14 salvation now came to the Gentiles through Jesus Christ.
And to make all men see what is the fellowship of the mystery, which from the beginning of the world hath been hid in God, who created all things by Jesus Christ:
More Questions
When was the mystery hidden in God?
The mystery/secret had been hidden since the beginning of the world, the ages, or Adam.