I suppose this is one of those "difficult" passages. Of course, Scripture was not written in the form of systematic theology and there are variouis theological emphases from the different writers. This passage deals with what theologians refer to as the "subordination" of the Son.
But, the passage implies this subordination is future. I think it's important to notice that it says:
then the Son himself will be made subject
Imagine if Paul was speaking of the Archangel Gabriel and had said:
"Gabriel will rule until all enemies are vanquished. Then, Gabriel will be made subject to..."
Wouldn't have Gabriel have been subject all along?
One interesting interpretation of this passage can be found here:
http://www.luthersem.edu/word&world/Archives/18-3_Trinity/18-3_Fredrickson.pdf
Notice particularly the last paragraph.
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