Ephesians 3:9

And to make all men see what is the dispensation of the mystery which for ages hath been hid in God who created all things.

To make all men see ... The message of salvation is to be preached to human beings, not angels, spirits or other non-terrestrial beings. It is important to keep this in mind in the study of the next verse.

The dispensation of the mystery ... Paul's many references in the New Testament to the mystery of God, the mystery of the faith, the mystery of Christ, the great mystery, the mystery of godliness, etc., etc., are among the most interesting passages in the New Testament. Essentially, Christ himself is the mystery, a thumbnail biography of Christ actually being called the mystery in 1 Timothy 3:16, the six several items of that biography being various elements of the mystery.

Which for ages hath been hid in God ... God's plan of human redemption existed always in the purpose of God, the fact of its being hidden indicating that there were beings who might indeed have understood it if God had chosen to reveal it. "God does not owe it to anyone to explain why for a long time the mystery was concealed."[23] It was concealed not only from the Gentiles, but also concealed from the Jews; and according to 1 Peter 1:12, it was also concealed from the angels in heaven. It was even concealed from the holy prophets of the Old Testament who were given revelations in words which they did not fully understand concerning this very mystery (1 Peter 1:10-12).

Hid in God who created all things ... The reason for injecting this word about the creation would appear to be "to indicate the relation of the matter in hand to the mightiest works of God. This is no trifling matter; it connects with God's grandest operations."[24] In fact, all through Paul's writings there prevails the impression that the saved in Christ are a part of infinite plans, all creation, even previous intelligent creations (as angels) being destined to share a common purpose with the redeemed when God shall sum up all things "in Christ." No pretense of being able to explain such things is affected by this writer.

[23] William Hendriksen, op. cit., p. 158.

[24] W. G. Blaikie, op. cit., p. 106.