sentence meaning question

Question

"'It seems probable that the foetus does not possess a rational soul as long as it is in the womb, and only begins to possess it when born, and consequently in no abortion is homicide committed.' Sextus V inflicted severe penalties for the crime of abortion at any period; these were in some degree mitigated by Gregory XIV, who, however, still held that those producing the abortion of an animated foetus should be subject to them, viz., and excommunication reserved to the bishop and also an 'irregularity' reserved to the Pope himself for absolution."

From WOMAN and THE NEW RACE - W.W. Norton

The highlighted part, I guess, implies some religious, Catholic, information, which I found beyond my understanding. Please help.

Answer 1

Let's start with some definitions...

to reserve to/for: Retain or hold (a right or entitlement), especially by formal or legal stipulation.

• with object and infinitive ‘the editor reserves the right to edit letters’

excommunicate: Officially exclude (someone) from participation in the sacraments and services of the Christian Church.

absolution: Ecclesiastical declaration that a person's sins have been forgiven. ‘she had been granted absolution for her sins’

In the Catholic Church, a local priest can hear confession and grant absolution for most sins. In some cases, he can also excommunicate a sinner. In other cases, those duties fall to some person with appropriate authority.

excommunication reserved to the bishop and also an 'irregularity' reserved to the Pope himself for absolution

Your quote states that for the "crime of abortion", only a bishop (or presumably someone higher up the chain) may impose the excommunication, and that only the Pope can grant absolution.