The Mormon church has published a rare interview with one of its "Twelve Apostles" justifying the decision to exclude the children of same-sex marriages from baptism.

Elder D. Todd Christofferson admitted to Michael Otterson, head of public affairs at the Church of Jesus Christ of Latter-day Saints, that the decision to update the handbook so children in a same-sex household may not be blessed or baptised as babies raised "difficult" and "sensitive" questions. 

"This is about family, this is about love and especially the love of the Saviour and how He wants people to be helped and fed and lifted, and that's the whole motivation that underlies our effort," he said about the widely-criticised decision.

He said the Church decided to update the handbook because Mormons regard same-sex marriage as a "particularly grievous or significant, serious kind of sin that requires Church discipline."

Discipline was mandatory in these circumstances, Christofferson added.

"We recognise that same-sex marriages are now legal in the United States and some other countries and that people have the right, if they choose, to enter into those, and we understand that. But that is not a right that exists in the Church. That's the clarification."

Asked about an apparently more tolerant tone from the Church on this issue in the past two years, Christofferson said that the recent decision of the US Supreme Court to make same-sex marriage a legal right meant a distinction now had to be made between what is legal in the secular world and what is the law of the Church.

"It's a matter of being clear, it's a matter of understanding right and wrong, it's a matter of a firm policy that doesn't allow for question or doubt."

As disciples of Jesus Christ they could yield no ground on this issue, he added. "That was the Saviour's pattern. He always was firm in what was right and wrong. He never excused or winked at sin. He never redefined it. He never changed His mind."

Speaking as a father and grandfather, he explained, the policy came out of compassion.

"It originates from a desire to protect children in their innocence and in their minority years."

For generations, this was how children in polygamous families have been treated, he said. He also noted that children could be baptised at 18, but only if they disavowed same-sex marriage. He said they would not have to disavow their parents. 

Jana Reiss, of Religion News Service, wrote that what she had wanted him to say was that it was not true that children would be denied baptism if their parent were in same-sex marriages. But in fact it was true.  She wrote: "I'm not sure which is more devastating: seeing the policy written in black and white, as I did yesterday, or hearing the gentle and avuncular Elder Christofferson, whom I admire, equate 'no baptism' to 'feed my sheep'. The latter, I think. I cried. Something in my heart shriveled when this kind man defended this policy on forbidding baptism as being what Christ would want."