Francis Sullivan said the letter called on all Church leaders to cooperate with the Commission and ensure all possible steps are taken to protect children and rid the Church of the scourge of sexual abuse of children.
"The message to the leaders of the Catholic Church around the world is that there is now no basis for maintaining the status quo, no turning back," Mr Sullivan said.
"The Pope has set a course to rid the Church of child sexual abuse regardless of the cost and the impact on reputations. It is now time for all Church leaders to get on board."
Pope Francis' letter asking the Catholic world's religious leaders for their full co-operation with the Vatican's Commission for the Protection of Minors is a positive sign of change in the Church.
Next month the Truth Justice and Healing Council will begin consultation meetings to discuss the establishment of an independent auditing body with broad organisational authority over all dioceses and religious orders regarding sex abuse issues
Royal Commission to hold private sessions in Newcastle
The Royal Commission into Institutional Responses to Child Sexual Abuse will hold private sessions in Newcastle from 24 – 27 February 2015.
Royal Commission CEO Philip Reed explained that private sessions are critical to the Commission's work, as they allow Commissioners to hear first-hand about the nature and prevalence of child sexual abuse.
Child sex abuse report finds 'unresolved trauma' costs nation
The Royal Commission has been contemplating the cost of a child sexual abuse as it prepares to recommend the establishment of a national redress scheme for survivors of abuse carried out inside the nation's churches, charities and other institutions.
A report commissioned by the advocacy group Adults Surviving Child Abuse (ASCA) into the economic impact of child abuse has found that it's already costing the nation more than $9 billion a year.
The report assessed the cost of providing services to help the estimated 5 million victims across Australia to deal with the long-term consequences of their trauma.