The nature of marriage is that, through its enduring bond, two persons together can find other freedoms, such as expression, intimacy, and spirituality. This is true for all persons, whatever their sexual orientation.

Those were the words of Justice Anthony Kennedy when he delivered the opinion of the United States Supreme Court last month, upholding the constitutional right of same sex couples to marry.

I was reminded of an earlier decision of the US Supreme Court, in 1967, in which it struck down laws which existed in several American states banning interracial marriage.

Like the referendum in Ireland, these milestones remind us that the principle of equality can overcome discrimination. They remind us of the simple power of the maxim equal treatment before the law.

In Australia today, two citizens who love each other and who wish to make a public declaration of their mutual and exclusive commitment through the ceremony of marriage are prohibited from doing so, solely on the basis of their gender.

No other attribute.

No other disqualification.

Simply because they are of the same gender.

If the disqualifying attribute were race, or age or religion, such a proposition would be seen as bizarre.

But it remains our law in respect of same-sex couples.

Archbishop Desmond Tutu has located the campaign to remove discrimination against lesbian and gay people with other campaigns against discrimination. He says:

Opposing apartheid was a matter of justice.

Opposing discrimination against women is a matter of justice.

Opposing discrimination on the basis of sexual orientation is a matter of justice.

Australians pride ourselves on our egalitarianism.

A fair go for all.

Equality is central to our egalitarian spirit, a part of our national identity.

We see the expression of this through our history.

Women were once denied the vote, were paid less and had to resign from our public service once married.

The children of Aboriginal Australians were once taken away.

Times have changed.

Misogyny and discrimination havent been eliminated, but are no longer entrenched in law.

The institution of marriage has evolved, too.

The Reverend Dr Margaret Mayman notes that marriage has its origins in the more mundane realities of property, procreation and patriarchy.

She observes: All over the western world, the movement to transform marriage is underway. However it is not gay and lesbian people who have been transforming marriage. It is heterosexuals. It is precisely because heterosexuals have changed marriage from an economic arrangement to a relationship of love and support that gay and lesbian people are seeking to join it.

I see progress too in different ways.

In the change in attitudes since I was first elected to our federal parliament.

In the easy going acceptance of the families and staff at our childcare centre.

In the generosity of the men and women who stop me in the street, or at the airport, from all walks of life, who tell me to press on.

In the kind emails and cards and gifts received when our daughters were born, not only from friends but from strangers.

And I see it in the many who have joined the campaign for equality.

Activists, business leaders, unionists, sporting heroes, the parents of gay and lesbian children, and so many more, have voiced their support for equality.

Its time our national parliament heeded the call for change from the Australian community.

Australians understand there is nothing to fear from equality.

Yet so many in our government stubbornly cling to discriminatory laws.

Over time the arguments against equality have become increasingly irrational.

The bogeyman of the slippery slope, or warnings about our relations with Asia, simply dont stack up as reasons to deny equality.

We also see the wellbeing of our children marshalled to the cause of discrimination.

Leave aside for a moment the truth that the quality of parenting is altogether more complex than simple assertions about gender.

The reality is this.

Same sex couples already have children.

Marriage equality will not alter that.

What continued inequality does is deny these children the opportunity to be part of a family which benefits from the stability and security of marriage.

As the Conservative Prime Minister of the United Kingdom, David Cameron, says, marriage equality is important because society is stronger when we make vows to each other and we support each other.

Let me deal with faith-based argument against marriage equality.

Remember that what we are proposing does not mandate marriage in our religious institutions.

It relates only to civil marriage, to the legal treatment of relationships by the secular state.

The proposition that those opposing want you to accept, is that the secular state, through its laws, should prohibit marriage between two people because of the religious tenets of some faiths.

Its a proposition which flies in the face of our philosophical and legal understandings of the relationship between church and state.

But beyond all of these arguments of principle, recall that this is more than a theoretical debate.

This is a debate about real people.

We are your brothers and sisters, your sons and daughters, your friends and your fellow Australians.

This is a debate about us.

A debate about rights.

A debate about intimate and personal relationships.

A debate about the people we love.

Most of us hope to find the person to share our life with.

The person we love.

Not all of us are lucky enough to do so.

Not all of us are able to hold on to it.

But if we do, and are prepared to make that commitment, to declare that enduring bond of which Justice Kennedy spoke, surely that ought be celebrated, not feared.

Do we really think, in 2015, that the state should say to people prepared to make that promise to each other, no you cant.

I say, it should not

.

Australians say, it should not.

If we succeed, most things wont change.

The sun will rise.

Heterosexual marriages wont crumble.

Three year olds will still want more ice cream than is good for them.

But together we will have made a profound change.

A statement to lesbian and gay Australians.

That we belong.

That we are accepted.

That our relationships matter too.

It will also be a statement about the Australia we have become.

An accepting, diverse and inclusive nation.

That, friends, is something to which we should aspire.