A lot of 20th century Catholic theology defines femininity in terms of 'active reception', and takes Mary as its model for this femininity: she was impregnated with Christ, but chose to allow God to work in her, to give birth to God in her. Thanks to Catholic theologians like Henri de Lubac and Hans urs von Balthasar, Mary become increasingly understood as the model for the church: to be a Christian is to actively receive God, to give birth to God in ourselves, both as a community and as individuals.
You'd think that this might make it easier to argue for the ordination of women: if Mary is the archetypal Christian, the model for the Church and, as some argue, even the model for the priesthood itself, it surely shouldn't be so difficult to imagine women as priests, right? Wrong. The argument generally goes something along the lines of C S Lewis's: we are all female in relation to God. De Lubac argues that the priest represents God to the Church and the Church to God, but that his role is primarily defined by his representation of God to the Church, and so just as God is male to the Church's female, so the priesthood is male to the laity's female.
Tina Beattie points out that the problem here is not that Catholic theology is unable to conceive of femininity and to understand its role in salvation and creation; the problem is the inability to really conceive of masculinity in the created world. Masculinity is associated with transcendence, reason and God; femininity with immanence, humanity and the body, but the result is that the only 'man' in creation is the priest, who represents the masculine divinity of Christ, and all other men are feminised: the bride but never the bridegroom.
Photo credit: Lincolnian on Flickr