Headship as being higher in rank, how does this harmonize with a trinity, when all are said to be equal ?
The Jehovah's Witnesses argue that Jesus could not have been God’s equal because Christ had a God above him and therefore God is superior in every way and Christ inferior, stating:
Not only is Almighty God, Jehovah, a personality separate from Jesus but he is at all times his superior. Jesus is always presented as separate and lesser, a humble servant of God. That is why the Bible plainly says that “the head of the Christ is God” in the same way that “the head of every man is the Christ.” (1 Corinthians 11:3) (Should You Believe, Chapter 7)
“Is not the sender superior to the one sent?” (ibid., Chapter 7)
First, as noted earlier, Trinitarians actually do believe that the created humanity of Jesus, who was not God, was a humble servant of God and inferior (see section 5).
Secondly, the Jehovah's Witnesses neglected to quote all of the relevant portions of verse 3, leaving out the reference to husband and wife which helps put these verses into proper context: “…the head of every man is Christ, the head of a woman is her husband, and the head of Christ is God.” The Greek word for ‘head’ is kephale and in this passage it is used “metaphorically, of the authority or direction of God in relation to Christ, of Christ in relation to believing men, of the husband in relation to the wife, 1 Cor 11:3” (Strong and Vine’s, 138). It is not intended to mean that one is inherently superior by nature to another as the Jehovah’s Witnesses would have you believe.
Paul is referring to authority possessed and exercised and an ordering of their relationship, but as the Jehovah's Witnesses interpret verse 3, a husband would be inherently superior as a person to his wife the inferior being, but we know that not to be true. In that culture, and in some contemporary matrimonial roles, the wife voluntarily assumes a particular subservient role. But just because a husband sends his wife down to the corner market for some milk, or the husband has the final decision with respect to, say, financial matters, that does not make his wife inferior to him as a person any more than the President of the United States is superior, as a human being, to any citizen of the United States of America. Your employer is not a superior individual, either, but only exercises authority over you.
The divine person of Christ, even if sent by God the Father, and even if He voluntarily subjected Himself, did not in so doing become less equal to God with respect to His essential being, nature and essence. When the Word assumed a human nature he did not cease being God, but willingly assumed a different relationship; a different grade, order or manifestation as Tertullian theorized. His incarnation and obedience did not diminish the divine essence of His being or make Him less consubstantial. The divine Person of Jesus was still fully God, who chose a veiled glory.
Christ possessed equality with God prior to His incarnation, and then for a time veiled that glory, being always God in all of the co-equal attributes, but in the incarnation never using His Godly powers to better Himself. He was fully God, fully man, God taking on the likeness of sinful flesh (Rom 8:3), not a man adding Godliness. (Strong and Vine’s, 42)
http://144000.110mb.com/trinity/index.html#3