1 Corinthians 15:27

For he hath put all things under his feet. But when he saith all things are put under him, it is manifest that he is excepted, which did put all things under him (KJV)

Then: This continued explanation of what's happening in the end times brings to mind both Psalm 110:1 and Psalm 8:6. The Corinthians had probably heard Paul discuss those verses before. The Holy Spirit reveals the meanings to all listeners. Paul is careful to point out that God, part of the triology is not a thing put under Christ. One part of the Godhead cannot be lower than another part.

Now: Commentators are sensitive to all Old Testament allusions because the Holy Spirit reveals the meanings. Some like Henry see a time when Christ works as a redeemer and is not in joint authority with God, the Father. Baker, (p. 223) disagrees. I can't think that it matters, but probably side with Baker. Each part of the triune God has specified work. They do it. The work does not affect standing or authority. God the Father, God the Son, and God the Holy Spirit are still one.

(Cf. - compare my work as a mother, wife, or daughter. By design, I am still one performing different tasks)

Extra Source: Commentary on the Whole Bible Acts to Revelation Vol VI by Matthew Henry online at http://www.ccel.org/ccel/henry/mhc6.iCor.xvi.html
Cornerstone Biblical Commentary 1 Corinthians (William Baker), 2 Corinthians (Ralph Martin & Carl Toney), ed. by Philip Comfort. Carol Stream: Tyndale House Publishers, c2006.