The Church "understands the desire of two people to express their commitment of love and self-sacrifice", and must accept the result should Australia vote for marriage equality, the head of the Anglican Church in Australia has said.

However, Church doctrine would not change, and would still consider marriage between a man and a woman, said Archbishop of Melbourne Philip Freier.

"Should the vote be in favour of same-sex marriage, as suggested by opinion polls, the Church must accept that this is now part of the landscape," he said in a letter to Anglican bishops.

"We can still stand for and offer holy matrimony between a man and a woman as a sacred ordinance given by God, while accepting that the state has endorsed a wider view of marriage... The doctrine of the Book of Common Prayer remains unchanged, that marriage is between a man and a woman, under God, forsaking all others until death parts them. I do not believe that the Anglican Church in Australia is likely to revise its doctrine of marriage."

Archbishop Freier added, however, that "Christians have not always shown the respect or perspective they should" regarding same-sex relationships.

"I am very concerned that the discussion does not become harsh or vilifying – on either side, for it is not only Christians who have sometimes failed on this score," he said.

"We understand that this is not a theoretical issue for many people, but one that directly impinges on their lives. We understand that sometimes gays, lesbians and others have felt judged and rejected, even ostracised, inside the Church and that we have to be much more pastorally sensitive in future.

"Whether this is the threshold event that many in our church think or whether the widening of marriage happened many years ago and further widening is inevitable remains to be seen. What does matter is that we approach this question with prayer, confidence in the Church's teaching as well as kindness in our speech towards those with whom we disagree."

It is not certain the plebiscite will go ahead as it's thought Labour may block the vote. According to the Sydney Morning Herald, attorney-general George Brandis will take a proposal to cabinet on Monday when Parliament returns.

A key figure in the pro-same-sex marriage movement has welcomed the Archbishop's letter, especially his call for Christians to "vote according to their conscience and their view of what is best for society".

"What you see in this statement is actually a real reflection of what the members of the church actually think," Tiernan Brady, head of Australians 4 Equality, said.

"It's real leadership to make this move and say clearly that it's OK to vote 'yes', and you can do in a way that's consistent with your belief."