Colossians 4:3-4

Colossians 4:3 At the same time pray for us too, that God may open a door for the message so that we may proclaim the mystery of Christ, for which I am in chains. 4:4 Pray that I may make it known as I should.

The word that stands out is mystery. What is this mystery?

From the beginning God allowed mankind to go his own way. We have been free to choose good or evil. For the most part, we have chosen evil. This comes with a price. Sin and death plague us.

But God had special mercy on one group: Israel.

His promises originally belonged to them, but they rejected (for the most part) the One whom God sent to save them.

As a result, they have become partially hardened. The hardening of Israel continues today. By and large, they have rejected Jesus.

As a result, God's promises were offered to the Gentiles until the full number has come in. What does that mean? God has a number of Gentiles that will be saved.

What next? After the full number of Gentiles comes in, the partial hardening of Israel will be lifted and Israel will return to God, through faith in Jesus Christ.

We were formerly disobedient, but have received mercy. Israel, disobedient as well, will receive mercy once again.
So the mystery, is this...God has opened the Gospel to the world. Whosoever will, let him take of the water of life freely! See Romans 11 for details.