Where was the mystery kept hidden since the beginning of the world?

Paul says the mystery was kept hid from the beginning of the world; it has been hid in God, the same God who created all things by Jesus Christ. This hiding was God's own prerogative, and He did it; the secret was not revealed from the world's beginning.

Les explains that this mystery, or secret, was hidden from the beginning of the world, or the age. Paul says it has been hid in God, the same God who created all things by Jesus Christ. The surrounding context ties this to God's ability and prerogative to hide things, a name of deity seen back in Genesis, and then moves to Colossians 1, where Paul speaks of being made a minister according to the dispensation of God to fulfill the word of God.

Ephesians 3:9

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:

Why was this mystery hidden from the beginning of the world, and where was it hidden?

Scripture says this mystery, or secret, was hidden from the beginning of the world because hiding is God’s prerogative; He is the everlasting God who is capable of hiding things. It was hidden in God, the same God who created all things by Jesus the Christ.