The mystery that Paul wrote about in Colossians 1:27 is not like the word we use. There are many mysteries that remain unsolved in human experiences. In verses 25-26 Paul wrote about the ministry God called him to.

The ministry to the Gentiles was given to him to fulfill the word of God. Verse 26 says, “The mystery which has been  hidden from ages and from generations, but now has been revealed to His saints.” 

This mystery was hidden in God’s heart all along. Verse 27 says, “To them God willed to make known what are the riches of the glory of this mystery among the Gentiles; which is Christ in you, the hope of glory.”

1 Corinthians 2:7-8 says, “But we speak the wisdom of God in  a mystery, the hidden wisdom which God ordained before the ages for our glory. which none of the rulers of this age knew…”