The significance of all things being brought under one head - Christ himself - is that through the death, burial and resurrectionof Christ, we will now experience the fullness of God, which without these events would not be there. It shows that Christ is the ultimate ruler and that all things will be subjected to his authority and rule. Christ is the key to our redemption, as we are instructed through the Word that we must come to God through Jesus.
This therefore relates to the Creator, because it comes back to the point that everything was created for the glory of God, in other words, everthing begins and ends in Jesus Christ.
This shows how important unity is in the body of Christ and how God intended us to live. Background or our past lives does not affect the ultimate purpose of grace, which places all born again Christians equal in Christ - into the same inheritance - through redemption, guided and directed by Christ Jesus. Not only that, but if we are not in unity with Christ as the head, then we fall outside of his rule and therefore have no place in the Kingdom of God.
This verse relates to 1 Corinthians 15:23-28 because it shows that ultimately everything has been placed under the authority of Christ. It also shows the unit between God the Father and Christ the son and that through Christ, God is in all. I think it brings across the importance of unity, not just in the Godhead, bu in the relationship between Children of God and Jesus, adn therefore brings a clearer understanding of the phrase "in Him" - which emphasizes that we as Christians cannot effectively operate separate and apart from Chist.