Brian Lucas, the senior churchman who former NSW premier Barry O'Farrell wants sacked, has been asked at a royal commission to explain his practice of not taking notes while interviewing abusive priests.

Fr Lucas, the general-secretary of the church's national body the Conference of Bishops, was making his second royal commission appearance in two weeks on Tuesday.

Justice Peter McClellan questioned Fr Lucas's practice at a Sydney hearing in which the commission is looking at how the Catholic Church, under its own canon law, deals with priests and others against whom allegations have been made.

As a member of the church's special issues committee in 1993, Fr Lucas interviewed John Gerard Nestor, a priest in the NSW Wollongong diocese, who was defrocked by the Vatican in 2008.

The senior cleric said on Tuesday that he did not take notes because it helped the men he interviewed tell the truth.

He also said he did not take notes after interviews but usually passed on the "outcome" of the conversation to the priest's superior over the phone.

Fr Lucas said the conversations were "very difficult, very robust", and taking notes would destroy the dynamic.

"I understand that but what about a note immediately after the conversation?" Justice McClellan asked.

Fr Lucas repeated what he said at the Cuneen inquiry in NSW and at an inquiry into the Marist brothers in Canberra last week: that he had promised confidentiality and taking a note after the conversation would have breached that.

Justice McClellan asked how it helped to persuade someone to admit they have done wrong if you tell them that you are not going to take a note.

Fr Lucas: "Because the consequence of them admitting that they have done wrong would be to move them to the next step."

The next step could be dismissal from the ministry, he said.

Justice McClellan asked him if he understood the "logical problem" with that approach, because if they told the truth there would be inevitable consequences.

He asked if his role was just to talk to a priest and pass on his denial or confession to his superior.

Fr Lucas said that, at that stage, he was just being asked by a bishop to do carry out a certain task.

In a speech to parliament last week Mr O'Farrell called for Fr Lucas to be stood down for failing to report child sexual abuse to police.

The former premier also criticised the church's response to Commissioner Margaret Cunneen's damning report in late May into the alleged cover-up of child sexual abuse in the Catholic diocese of Maitland-Newcastle.