And he had power to give life unto the image of the beast,
that the image of the beast should both speak,
and cause that as many as would
not worship the image of the beast should be killed.
Revelation 13:15
"Historically, Catholic theologians have given three main arguments in favor of the death penalty.
The first is that justice demands it for certain offences. Every injustice creates an imbalance, and justice, say the theologians, demands that the imbalance must be corrected.
Second, the Church has taught that the death penalty is expiatory. Expiation is an attempt to redress, through penance and other forms of mortification, some wrongdoing. Catholics are taught that we must achieve expiation either here or in the cleansing fire of purgatory.
As Pope Pius XII said: “It is reserved then to the public power to deprive the condemned man of the benefit of life, in expiation of his fault, when already, by his crime, he has dispossessed himself of the right to life.”
Third, the death penalty can sometimes support the common good. St Thomas Aquinas makes this point: “Therefore if a man be dangerous and infectious to the community, on account of some sin, it is praiseworthy and advantageous that he be killed in order to safeguard the common good.”
It is no coincidence that the increasing rejection of the death penalty has coincided with a decline in religious practice and belief in an afterlife. If there is no God, and no punishment or purgation in the afterlife, then there is no need for expiation, and injustice becomes not a cosmic imbalance with implications that spread to eternity but a simple transaction payable only in this one terminable lifetime." Catholic Herald