Op's question:
A. Does this mean, to unite all things which are already "in him", but separate, as some are in heaven and some on the earth.
B. Or, to unite all things into Christ's headship including those things which are not "in Christ".
Great question. Basically it boils down to are ALL things going to end up being in Christ where uniting things on heaven and earth can even take place.
having made known to us the secret of His will, according to His good pleasure,
that He purposed in Himself,
In regard to the dispensation of the fulness of the times,
to bring into one
the whole
in the Christ,
both
the things in the heavens,
and the things upon the earth — in him;
First of all we have to see that this is a secret or mystery that has never been revealed until Paul writes these words.
3466 mystḗrion (the root of the English term, "mystery") – mystery. In the Bible, a "mystery" (3466 /mystḗrion) is not something unknowable. Rather, it is what can only be known through revelation, i.e. because God reveals it.
This is going to give God great pleasure to see this happen because he purposed it in Himself.
This word purpose is used only three other times in the New Testament.
◄ 4388. protithémi ►
Strong's Concordance
protithémi: to set before,
Original Word: προτίθεμαι
Part of Speech: Verb
to set before, propose
Usage: I purpose, design beforehand, determine.
Cognate: 4388 protíthemai (from 4253 /pró, "towards" and 5087 /títhēmi, "to place, set") – properly, to place before, setting forth in advance to achieve a particular purpose.
[4388 /protíthemai ("to purpose") is the root of 4286 /próthesis ("God's providence, eternal purpose)
This is going to give him a great pleasure to do this. It is something that he purposed in Himself.
This is what He purposed:
with regard to the fulfillment of the times [that is, the end of history, the climax of the ages]—to bring all things together in Christ, [both] things in the heavens and things on the earth.
This plan, which God will complete when the time is right, is to bring all creation together, everything in heaven and on earth, with Christ as head.
in regard to the dispensation of the fullness of the times, to bring into one the whole in the Christ, both the things in the heavens, and the things on the earth—in
Pulling from a few other scriptures might shed meaning to that.
Philippians 2:10
that at the name of Jesus every knee should bow, in heaven and on earth and under the earth,
Colossians 1:16
For in Him all things were created, things in heaven and on earth, visible and invisible, whether thrones or dominions or rulers or authorities. All things were created through Him and for Him.
Colossians 1:20
and through Him to reconcile to Himself all things, whether things on earth or things in heaven, by making peace through the blood of His cross.
Scripture shows is that everything was created through him and for him and he's going to reconcile ALL things.
Things in the heavenly realm need to be reconciled to him as well. That's where this administration that is brought to light in the book of Ephesians will have a big part in this heading up.
The grace that was bestowed on someone who believes now, had been called out for a purpose to be part of Christ 's body heading up those in the celestial realm where we have all of our celestial blessings.
In all wisdom and insight He made known to us the mystery of His will, according to His kind intention which He purposed in Him with a view to an administration suitable to the fulness of the times, that is, the summing up of all things in Christ, things in the heavens and things upon the earth (Ephesians 1:8
As unflattering as it may be to the human ego, the coming of Christ was not only to save men from their sins. According to Ephesians, man’s salvation is not the ultimate purpose of the coming of Christ. God’s eternal purpose is the “summing up of all things in Christ.”
This happened because he made known to us the once hidden but now revealed secret of his will, for so it was his good pleasure to do. The secret was a purpose which he formed in his own mind before time began, so that the periods of time should be controlled and administered until they reached their full development, a development in which all things, in heaven and upon earth, are gathered into one in Jesus Christ (Ephesians 1:8-10, Barclay’s paraphrase).21
The purpose of God in history is to bring glory to Himself by bringing all of creation under the headship (the authority and rule) of Christ.
For from Him and through Him and to Him are all things.
To Him be the glory forever! Amen.
and when ALL things have been subjected to Him, then the Son Himself will be made subject to Him who put all things under Him, so that God may be ALL in ALL.
In Christ, Everything is perfect, and makes it possible for God to fill each creature with Himself!!!!
Could it be that this is what Christ was looking forward to on the cross?