Australian Prime Minister Kevin Rudd has clashed with a Christian pastor over gay marriage, using the Bible to support his argument as he explained his change of heart on the issue.
Labor leader Rudd, who is lagging in polls ahead of Saturday's national election, was asked why Christians should vote for him given "Jesus said a man shall leave his father and mother and be married, and that's the Biblical definition".
"I'm just curious for you, Kevin, if you call yourself a Christian, why don't you believe the words of Jesus in the Bible?" pastor Matt Prater asked the prime minister on the live programme "Q&A" on Monday night.
"Well, mate if I was going to have that view, the Bible also says that slavery is a natural condition," Rudd responded to sustained applause.
"Because St Paul said in the New Testament, slaves be obedient to your masters. And therefore we should have all fought for the Confederacy in the US Civil War. I mean, for goodness' sake."
Gay marriage is a key issue in some electorates, with Rudd becoming the first Australian prime minister to go into an election promising marriage equality, vowing to introduce a bill legalising the unions if returned to office.
Conservative opposition leader Tony Abbott is opposed to same-sex marriages.
Rudd last year voted against gay marriage in parliament, but has since changed his mind, prompting Prater to ask whether the prime minister kept "chopping and changing your beliefs just to get a popular vote with regards to things like marriage".
"The human condition and social conditions change," Rudd said, adding that his conversion was the result of "many months and years of reflection in good Christian conscience".
He said the fundamental principle of the New Testament was one of universal love, "and if we get obsessed with a particular definition of that through a form of sexuality, then I think we are missing the centrality of what the gospel... is all about".
"And if you think homosexuality is an unnatural condition, then frankly I cannot agree with you," he added.
Same-sex unions are available in a majority of Australian states but because marriage comes under federal legislation these couples are not formally recognised as married by the government.