Male and female as the image of God

God created man in his own image, in the image of God he created him; male and female he created them (Genesis 1:27).

According to Frances and Paul Hiebert, the humanity that images God is a co-humanity constituted by men and women in relationship. Stated negatively, men alone and women alone do not express fully the image of God (see the Hiebert's essay, The Whole Image of God: A Theological and Anthropological Understanding of Male-Female Relationship, in Incarnational Ministryedited by Kettler and Speidell).

This makes sense in light of the biblical revelation that our triune God is a relational communion of three persons (Father, Son and Holy Spirit), in which there is unity, diversity (distinction of persons) and equality. God's communitarian nature is imaged in humanity when a similar unity, diversity and equality are found in us - particularly in our male-female relationships.

According to the Hieberts, differing male and female reproductive functions produce a unity-in-diversity expressed in "one flesh" intimacy (p270). God's intent in this is shown in the first chapters of Genesis. There all that God creates he pronounces "good," with the exception of Adam in his state of aloneness. This is intentional, but subsequently resolved by God when he creates woman - recognized by man as his equal ("bone of my bone and flesh of my flesh"), sharing both his strengths and weaknesses. The Heiberts comment:
They each shared the full spectrum of human characteristics. But because either of them alone would have been 'not good,' they were made to be mutually interdependent. They were "for" each other - "for" in the sense of being in support of, not in the sense of being used by (p271).  
God gave the woman to the man to be his "helper" (Heb='ezer; Gen 2:18) - not a role of inferiority or servitude, but an exalted role like that filled by God himself, who in Exodus 18:4 is called our "Helper" ('Ezer). Indeed, the original design for the woman with the man is that of co-equality:
When everything still was good in God's creation, the man and the woman, thrilled by the discovery of their mutual humanity, were fully equal. They both mirrored the image of God; they both were honored by God with the gift of responsibility for the earth. With singing hearts, they lived in harmony with God, with each other, and with the rest of creation" (p272).
Sadly, their disobedience changed everything. The image of God in their co-humanity was splintered as the relationship between woman and man was shattered and "the world is still reeling from that terrible, cosmic disaster" (p273). And though it is typically understood that this disaster brought alienation between God and humans, it is less well understood that it also brought alienation between humans, particularly between men and women.

In the New Testament, male-female alienation is seen principally as conflict instead of cooperation. In defending their self-interest in this conflict, men tend to dominate, while women tend to manipulate. Both approaches express the twin sins of pride and independence. Thus the New Testament solution is restoration and reconciliation, which stand at the heart of the gospel (Col 1:15-20):
The broken body and shed blood of Jesus restores the broken image to wholeness; what was lost in Eden is recovered by his life, death, and resurrection. Because of Jesus, it is possible for humans to be reconciled to God and to each other, male and female, and to live in the awareness of what God means by good through the strength of the indwelling Spirit of God.... In the new era inaugurated by Jesus, man and women, rather than being at war for the dominant position, are restored to the position of equality that constituted their life before the fall (pp 274-5).
In Christ, men and women are set free to be "equal to" one another in order that they may be "for" each other as God originally intended. According to Jesus, the appropriate metaphor for this is being a servant of one another, rather than lord (Mat 20:25-28). Indeed, the way Jesus treated women was an indication of this restored equality within the kingdom of God. Sadly, this was not practiced by the early church for long. This was largely because the church embraced the deprecation of women as practiced by surrounding peoples.

But the church is called to live in this present age out of the truth of the image of God, revitalized by the breath of God, the Holy Spirit. History shows that when it does so, men and women begin to relate more as equals. This is seen in the New Testament record, and in church renewal movements since. For example, there was a significant move toward female ordination during the American Great Awakening of the 18th century in the northeastern United States. Breathe on us breath of God!