Archbishop of Dublin Dr Diarmuid Martin has said that some people in the Catholic Church may be homophobic.
The teaching of the church could be used “in a homophobic way”, he told RTE.
He said that the Church had to be very careful that this was not done in the forthcoming debate on the same-sex referendum.
Archbishop Martin said he felt that the debate had already got off to a bad start.
Discussions have to be carried out in a “mature” way so that people can freely express their views, while at the same time being respectful and not causing offence, he said.
He said that in general he believed it was the person who was offended who defined what being offended is.
“Anyone who grew up in Ireland would have told jokes that were pointed at the gay community; at Travellers; it is part of the culture we grew up in, but we have to grow out of it,” he said.
He said church teaching was that marriage was between a man and a woman, exclusively, but that this approach did not exclude gay people from celebrating their union by a different means.
The Government has agreed to hold a referendum on civil marriage for same-sex couples in the first half of 2015.
Last April, the Constitutional Convention voted overwhelmingly to recommend that the constitution be changed to allow for civil marriage for same-sex couples.
In June, the convention submitted its report to the Government.
Tanaiste Eamon Gilmore earlier said the right of gay people to marry was an “important issue”.
Mr Gilmore said it would be “important to win this referendum”.