The Catholic church is a "law unto itself" in need of serious cultural reform if it is to properly address widespread allegations of child sexual abuse within its ranks, a royal commission heard.

The Catholic Archbishop of Brisbane Mark Coleridge told the Royal Commission into Institutional Responses to Child Sexual Abuse there was a lack of transparency within the church.

"We are, as it were, a law and a world unto ourselves," he said.

The third day of the three-week public inquiry into Catholic church authorities is examining the factors behind clerical sexual abuse.