Harry Benson, research director at the Marriage Foundation, made the comment before MPs vote on a bill this week that would legalise heterosexual civil partnerships.
Benson, who is a Christian, told Premier News Hour: "For the tiny minority of people who don't get married for some obscure sort of ideological reason, this is a way for them to express the same commitment that you get in marriage but just call it a different name.
"I think we can afford to be a little gracious on these sorts of issues."
Benson said some couples want a civil marriage because "there's a historical hangover" of people thinking marriages are bad, instead of "attributing it to bad people".
Because of this ideology, Benson said Christians should be gracious. He also said this law wouldn't be anti-marriage.
"As a Christian I think this is us being gracious about this issue and also being sensible and pragmatic," he said.
"In no way will this undermine marriage for one second. It's all about lifelong commitment. It's all about encouraging couples to make a formal commitment to one another in exactly the same way you would make the Biblical idea of covenant."
The bill, which has cross-party support, would affect more than 3 million couples if approved.
Listen to Harry Benson speaking with Premier's Eno Adeogun here:
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