“To me, the least significant of all the saints, this grace was given to declare to the nations the incomprehensible riches of Christ and to give light for all of the plan of the mystery hidden from the ages in God who created all things, in order that the manifold wisdom of God through the church may now also be made known to the authorities in heavenly places, according to the eternal purpose that he has realized in Christ Jesus our Lord in whom the boldness and freedom to enter with confidence through faith in him.”
It may seem that we are beating a dead horse with this idea, but if we are beating a dead horse, it is only because Paul keeps bringing it up. From when has the mystery of the Gospel been hidden in God? Paul writes that it has been hidden “from the ages.” The Greek word used in this case is αἰών (aion), which is the origin of the English word, eon. This word refers to the ages past or to the beginning of time — “the earliest ages” as the scholarly lexicons would read.
While it is true that this term does not need to refer to eternity past and can speak of long ages ago, the same point can be made. God has sovereignly chosen and decided his mystery — his plan of the Gospel and to redeem the Gentiles as amongst his people — from the ages. God did not change his mind and include the Gentiles when the Jews refused the Son as many dispensational theologians would teach. He also decide the best course of actions in response to human choices as open theists and free-will theologians would teach. God ordained a plan from old and worked out that plan in time and space, revealing it ultimately in His Son and proclaiming it through the Apostle Paul and through others. God had his plan before the foundations of the earth, as Paul has already mentioned in this letter, and is working it out in time.