Why cardinals have ranks, and how Pope Francis changed them

Pope Francis made an unexpected change Tuesday in the structure of the College of Cardinals, adding some curial officials to the rank of “cardinal bishops,” the highest rank within the college.
The College of Cardinals is structured in three orders, or ranks: the order of “cardinal deacons,” the order of “cardinal priests,” and the order of “cardinal bishops.”
There are customarily six cardinal bishops from the Latin Church, who are given a particular ceremonial title as the “titular bishops” of Rome’s ancient suburbicarian sees. The dean of the College of Cardinals is also assigned as titular bishop of the Roman see of Ostia.
Eastern Catholic patriarchs who are cardinals are also cardinal bishops.
Though, in modern times, cardinal bishops do not actually govern the suburban dioceses in the vicinity of Rome, the custom of corresponding the rank of cardinal bishop to those dioceses is ancient.
The pope’s new appointments break with that custom, which is established in canon law, as he has appointed cardinal bishops who will not be ceremonially connected to those suburbicarian sees. In fact, those sees already have titular bishops, each of whom is a cardinal bishop over the age of 80, the age at which cardinals are no longer eligible to vote in the conclave that elects a pope.
Those elevated to the rank of cardinal bishop are Cardinal Pietro Parolin, Vatican Secretary of State; Cardinal Leonardo Sandri, Prefect of the Congregation for the Eastern Churches; Cardinal Marc Ouellet, prefect for the Congregation of Bishops; Cardinal Fernando Filoni, Prefect of the Congregation for the Evangelization of People.
Among these new cardinal bishops, Cardinal Filoni was until now a cardinal deacon, while the others were all cardinal priests.
The Pope’s June 26 rescript says that popes have “always looked with fraternal fondness to the College of Cardinals,” as they “offer a particular support to the mission of the Successor of Peter, bearing the valuable contribution of their experience and of their service to the particular Churches spread all over the world.”
The rescript then noted that “in the last decades” the College of Cardinals has expanded, thus increasing the number of cardinal priests and deacons, while the number of cardinal bishops has stayed untouched with time, and so the pope made the decision to expand that group.
The decision derogates from canons 350 and 352 of the Code of Canon Law, and will come into effect since the next June 28.
All three ranks within the College of Cardinals have ancient historical roots. Cardinal deacons were anciently entrusted with the administration of the six offices of the Lateran Palace (the See of the Bishop of Rome, the Pope) and of the the seven departments of Rome, including care for poor. After Pope Sixtus V, they became 14, two for departments, and were given a “deaconry” of administration, that is, a church in Rome for which they were responsible.
The cardinal priests were those entrusted with the care of the most ancient Churches in Rome, called “titles,” and are by tradition connected with a Roman parish. After ten full years as a cardinal deacon,”a cardinal can “opt” to become a cardinal priest.
There were originally seven cardinal bishops, the bishops of Rome’s suburbicarian sees.
The present cardinal bishops, in addition those named today, are Tarcisio Bertone (Frascati), José Saraiva Martins (Palestrina), Roger Etchegaray (Porto Santa Rufina), Giovanni Battista Re (Poggio Mirteto) and Francis Arinze (Velletri-Segni).
Cardinal Patriarchs of Eastern Catholic Churches, who are also cardinal bishops  are Patriarch Bechara-Boutros Rai, of Antioch of the Maronites; Patriarch Pierre Sfeir, emeritus of Antioch of Maronites; Patriarch Antonios Naguib, emeritus of Alexandria of the Coptics.
Cardinal-Elect Louis Raphael Sako, Patriarch of Babylon of the Chaldeans, will be added to the list after the June 28 consistory.
The Pope choose to expand the rank of cardinal bishop  to include the prefects of some Vatican offices, although some notable prefects are missing from the list.
Some have speculated that Cardinal-elect Luis Ladaria is likely to be appointed to the order of cardinal-bishop, as is as Cardinal-elect Konrad Krajewski, Papal Almoner.
In a recent interview with Reuters, Pope Francis said:  “It think there are two long arms of the pope – that of being custodian of the faith, and there the work is done by the Congregation for the Doctrine of the Faith, and the prefect has to be a cardinal, and the other long arm of the pope is the almoner, and there must be a cardinal there. These are the two long arms of the pope – faith and charity.”
Another rescript will be needed if the Pope wants to derogate again from the norms of canon law, in order to include other cardinals in the rank of cardinal-bishop.
Far from being just honorific titles, the ranks of cardinals give them specific obligations.
For example, the Dean of the College of Cardinals, elected from among the cardinal bishops, presides at the conclave for the election of the pope. The Dean has also the responsibility to communicate the pope’s death to the diplomatic corps accredited to the Holy See and to the heads of nations, he represents the Holy See during the sede vacante, and he is the one who asks the pope-elect if he accepts the election, and what name he will take.
If the new pope is not a bishop, the Dean has the right to ordain him.
If the Dean is older than 80, and so not eligible to take part in the conclave, the senior cardinal bishop presides over the conclave.