God's Gospel as it pertains to Christ is the doctrine of the Administration of Grace
that was kept secret in God until revealed to the Apostle Paul.
It is this administration that is God's purpose of the Ages.
And to make all men see what is the fellowship [oikonomia = administration]
of the mystery, which from the beginning of the world [aion (plural) = ages]
hath been hid in God, who created all things by Jesus Christ: To the intent
that now unto the principalities and powers in heavenly places might be known
by [dia = through] the church the manifold wisdom of God, according to the
eternal purpose which he purposed in Christ Jesus our Lord:
The words in red are not in the manuscripts.
The foundation of the doctrine for the Administration of Grace is the Epistle to the Romans.
After revealing some of the things God had hidden in Himself,
He closes this amazing epistle with these words.
Now to him that is of power to stablish you according to my gospel, and the preaching
of Jesus Christ, according to the revelation of the mystery, which was kept secret since the
world began, but now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith [active believing]: