Like the most Australians, I support marriage equality. I do not believe our current definition of marriage reflects the modern, generous and inclusive nation we love. It sends the wrong message to the world and to young Australians.

But I understand that not every Labor MP or party member feels the same way. Some, particularly people of faith, take a different view. I respect this. It's why I support a free vote on marriage equality.

Solidarity still has powerful meaning in our party and a binding vote would put a handful of Labor MPs in a very difficult position. Either they vote against their conscience, or they vote against the party they've dedicated their working life to serving.

I was proud to move, with by deputy Tanya Plibersek, Labor's historic Bill in June to reform the definition of marriage. But even if every Labor MP in the House of Representatives were forced to vote in favour of our marriage equality legislation, there would not be enough votes in the Parliament to make marriage equality law.

I believe the best way to ensure our Parliament passes a definition of marriage which includes, values and respects every Australian relationship is for all representatives, from all parties, to have a free vote. Liberal, Labor, National, Green and independent MPs all deserve the chance to engage with this issue.

I believe a free vote, or "conscience vote", will foster the respectful, considered and diverse conversation the matter of marriage equality deserves. I'm hopeful Tony Abbott will allow his MPs a free vote when Parliament returns, to achieve this outcome.

If Labor gets hung up on procedural argy-bargy, we jeopardise this possibility. Not only is it far more difficult for us to call on Tony Abbott to give his party room a free vote if we bind ourselves, there is also the risk that the Coalition re-commits to binding against marriage equality.

In Australia, and around the world, marriage equality has come a long way. The referendum in Ireland and the decision by the United States Supreme Court have added vital morale and momentum to the Australian cause.

Frequently now people speak of marriage equality as an "inevitable" social change. In my experience, there is no such thing as inevitable progress, and worthwhile change is always hard-won. The best way to deliver reform is to bring people together. To build support by finding common ground; through consensus not coercion – not through the force of procedure but through the power of an idea whose time has come.

I believe it will be a proud day when Australia embraces marriage equality, an uplifting moment. All of us who support this overdue act of justice have a responsibility to focus on the best way of achieving it: a free vote for every member of our nation's parliament.

This article was originally published in The Age online on Thursday, 23 July 2015.