Here's how I'm seeing it (briefly):
--the "FOR" (regarding the "whom" in v.29) points back to the "
those according to
His purpose [G4286]
being [present participle] called [G2822]"...
... and same book in Romans 1:6,7 says "6
called [G2822] of Jesus Christ" and "7
called [G2822] saints".
...and in 1Cor1:24 says, "to them the
called [G2822] both Jews and Greeks"...
... and see also 1Cor1:2 and Jude 1:1 and how they use this same word -
https://biblehub.com/greek/2822.htm
So then the question becomes, to what does the word (in Rom8:28) refer, where it says "[those according to
His]
PURPOSE - G4286 [
being called - G2822]"...
... and we see some of this in the following passage:
8To me [Paul], the very least of all saints, was given this grace: to preach to the Gentiles the unsearchable riches of Christ
9and to enlighten all what
is the administration of the mystery having been hidden from the ages in God, the
One having created all things,
10so that now through the church the manifold wisdom of God should be made known to the rulers and authorities in the heavenly realms,
11according to the purpose - G4286 of the ages, which He accomplished in Christ Jesus our Lord,
12in whom we have [...]