The secret of the gospel

Colossians 1:24-29
 I have become its servant by the commission God gave me to present to you the word of God in its fullness.
To them God has chosen to make known among the Gentiles the glorious riches of this mystery, which is Christ in you, the hope of glory.
He is the one we proclaim, admonishing(勸告) and teaching everyone with all wisdom, so that we may present everyone fully mature in Christ.
The apostle's job is to make God's message known. The philosophers hint at secrets, at deep things known only to the initiated. This is God's open secret: Christ - in you!'
A share in God's own glory for every Christian! This is a 'secret' worth knowing.
It makes all Paul's struggle and effort 'to preach Christ to everyone' worthwhile.
Why?
Paul applied to himself the same pattern, of suffering on behalf of others, that was worked out on the cross. He is not adding to that work: Christ's saving work is complete. But in the overlapping of the ages, between Christ's resurrection and his return, God's new people will suffer as their Master did.
Secret: Paul called the the word of God and Jesus Christ as secret. Remind and encourage to dig out more about the secret to present fully mature in Christ.
How?
Nothing is important than knowing Christ Jesus. What I need to do is study more hard to read the word of God and meditate God's will and present fully mature in Christ.