Is God capable of hiding things, and is hiding His prerogative?
Yes. The God who is everlasting is capable of hiding things, and doing so is His prerogative. Paul says the mystery was kept hid in God from the beginning of the world, and the same God created all things by Jesus Christ. This hiding was His own doing and prerogative.
Les explains that one of the names of deity back in Genesis presents God as everlasting, yet He is capable of hiding things, and that is His prerogative. In the Ephesians passage, Paul says the mystery or secret had been hid from the beginning of the world or age, and it was hid in God, the same God who created all things by Jesus Christ. Les then moves to Colossians 1, where Paul rejoices in sufferings for Christ's body, the church, and says he was made a minister according to the dispensation of God given to him to fulfill the word of God.