Ephesians 3:3 That by revelation the mystery was made known to me... (4) ...the mystery of Christ, (5) Which in other generations was not made known to the sons of men, as it has now been revealed... (6) That in Christ Jesus the Gentiles are fellow heirs and fellow members of the Body and fellow partakers of the promise through the gospel, 1:23 Which [the church] is His Body, the fullness of the One who fills all in all.
In the New Testament we have the revelation, the unveiling, of God's economy [plan]. In other ages and generations this economy was a hidden mystery. It was not made known to Adam, to Abraham, to Moses, to David, or to Isaiah and the other prophets.
If they had been asked what God's economy is, they would have been unable to answer, for during their time the mystery was still veiled. God's economy, the dispensing of Himself into man to produce a Body for His Son, had not been revealed to them. The Son of God is the embodiment of God.
God's economy is to dispense Himself into a great number of human beings in order to produce a Body for this embodiment of Himself. This means that the Son of God as the embodiment of God requires a Body, an increase, an expansion. This expansion can be produced only by God's dispensing of Himself into His chosen people.
This is the greatest mystery in the universe... We know that God's economy is to dispense Himself into His chosen people in order to produce the Body as the expansion of the Son of God for the full expression of God in the universe. Nothing is greater or more important than this...
By revelation this great mystery, which had been hidden until the coming of the Lord Jesus, has been unveiled to us.