If I understand correctly, the Pope has the power to dissolve (not just retroactively annul) a marriage which has not been consummated. What’s the theological grounds behind this idea, and why does it apply specifically to the Pope but not to the other bishops?
A valid marriage that is unconsummated can be dissolved because the couple has not become one flesh yet through the conjugal act. However, since matrimony is favored, it requires an examination. A dispensation is reserved to the Supreme Pontiff, but the bishops vote. The reasons are given in Pastor Bonus.
CIC
Can. 1061 §1. A valid marriage between the baptized is called
ratum tantum if it has not been consummated; it is called
ratum et consummatum if the spouses have performed between themselves in a human fashion a conjugal act which is suitable in itself for the procreation of offspring, to which marriage is ordered by its nature and by which the spouses become one flesh.
Can. 85 A dispensation, or the relaxation of a merely ecclesiastical law in a particular case, can be granted by those who possess executive power within the limits of their competence, as well as by those who have the power to dispense explicitly or implicitly either by the law itself or by legitimate delegation.
Can. 87 §1. A diocesan bishop, whenever he judges that it contributes to their spiritual good, is able to dispense the faithful from universal and particular disciplinary laws issued for his territory or his subjects by the supreme authority of the Church. He is not able to dispense, however, from procedural or penal laws nor from those whose dispensation is specially reserved to the Apostolic See or some other authority.
**Pastor Bonus
**
Article 126
§ 1. The Roman Rota is a court of higher instance at the Apostolic See, usually at the appellate stage, with the purpose of safeguarding rights within the Church; it fosters unity of jurisprudence and, by virtue of its own decisions, provides assistance to lower tribunals.
§ 2. An Office has been set up at this Tribunal to examine the fact of non-consummation in a marriage and the existence of a just cause for granting a dispensation. It therefore receives all the acts, together with the
votum of the Bishop and the remarks of the Defender of the Bond, weighs them according to its own special procedure and, if the case warrants it, submits a petition to the Supreme Pontiff requesting the dispensation.
§ 3. This Office is also competent to examine cases concerning the nullity of sacred ordination, in accordance with both universal and proper law,
congrua congruis referendo”.
Article 4
The Office for processes of dispensation from ratified and non-consummated marriage and for cases concerning the nullity of sacred ordination is presided over by the Dean of the Roman Rota, assisted by Officials, Delegated Commissioners and Consultors.