Tom Frame, Church and State: Australia's Imaginary Wall (Sydney: UNSW Press, 2006).
Frame's slim book (96 pages) adopts a middle-ground on the debate over the relationship between church and state in Australia. He argues that both the Christian majority and the secular minority should refrain from extremist positions. For Christians, Frame supports his argument with a reference to both history and theology:
"It can be said with some certainty, however, that there is nothing in the Bible or in Christian history which justifies or encourages the fusion of church and state. It harms religion and distorts the church. While it might be appealing to Christians starved of social or political influence to embrace the state, merging church and state into a single entity would not deliver what its advocates promise." (p. 31)
For secularists, Frame argues:
"Australia does not need a wall of separation between church and state, and none will be needed in the near future if the recent past is any guide." (p. 95)
Overall, Frame suggests that Christians focus on spiritual outreach and reformation of individuals instead of trying to coercively influence public life through government support, while simultaneously suggesting that secularists be content with non-coercive, non-denominational governmental displays that reflect the heritage of the Christian majority.
In regards to the religious beliefs of Australians, Frame offers an interesting perspective:
"I concluded some time ago that Australians are generally indifferent to religious concepts, other than when they might demand some moral response, and that they are spiritually unresponsive. To the vast majority, religion is largely about formalised rituals of commemoration. Spirituality is just another dimension of therapy for those so inclined. A scent of Christianity continues to pervade the public sphere but it is fading fast." (p. 67)
It is a brief book, but it is definitely well-research and well-written. Trying to summarize the evolution of Christianity on the separation of church and state globally in fifteen pages is an impossible goal, but Frame does about as good a job as is possible. There's also a brief summary of how the Australian Constitution and High Court treat religion, which is also useful for a quick overview.