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What Does Paul Mean: “Christ Will Reconcile to Himself All Things”?
Some have used Colossians 1:20 to argue for universalism — that all rebel creatures, including the devil will be reconciled to God in the end and there will be no eternal hell.
In him all the fullness of God was pleased to dwell, 20 and through him to reconcile to himself all things, whether on earth or in heaven, making peace by the blood of his cross.
What's Said Elsewhere
I don’t think such universalism fits with what Jesus or Paul or John say elsewhere. Nor is it a necessary meaning of Colossians 1:20.
Jesus says that there are some who “will go away into eternal punishment, but the righteous into eternal life” (Matthew 25:46).
Paul said there are some who “will suffer the punishment of eternal destruction, away from the presence of the Lord” (2 Thessalonians 1:9).
John says of these that “the smoke of their torment goes up forever and ever” (Revelation 14:11).
"All Things" Then, Not Now
One of the reasons some think Colossians 1:20 says something different from these three texts is that it's assumed Paul means “all things” in the universe now will someday be reconciled to God. I don’t think he means that.
I think he means that the blood of Christ has secured the victory of God over the universe in such a way that the day is coming when “all things” that are in the new heavens and the new earth will be entirely reconciled to God with no rebel remnants.
Before that day comes, all those who refuse to be reconciled by his blood will be cast into “outer darkness” (Matthew 8:12), so that it is not reckoned to be a part of the new heavens and the new earth.
The rebels in hell will simply not be part of the “all things” which fill the new heavens and the new earth. They are “outside” of the new reality, in the “darkness.”
Heinrich Meyer explains Colossians 1:20 in the same way. He puts it like this.." from the article: What Does Paul Mean: “Christ Will Reconcile to Himself All Things”?