A group representing clergy who support gay marriage believes making it legal will be good for society.
Parliament's Government Administration Committee is hearing submissions on a Member's bill to make same-sex marriage legal.
Christians for Marriage Equality told MPs the current law is discriminatory and gay marriage will allow more social respect for all couples.
Spokesperson Margaret Mayman says it is only the state stopping churches that want to marry gay couples.
Ms Mayman says marriage is evolving, but it is still about responsibility and commitment and including more gay people in the institution would be good for society.
Earlier, one of the first couples in New Zealand to have a civil union say that was a compromise and only being able to marry would give them equality.
John Jolliff and Des Smith, who have been together for more than 25 years, say they are just ordinary gay guys who have been treated in a less than ordinary way by the law.
Mr Jolliff says legal discrimination against homosexuals is not fully gone, given that only heterosexual people can opt to have a civil union and/or marriage.
Mr Smith says allowing gay marriage would help break down insidious homophobia.