Since Pope St. Paul VI, the Magisterium has consistently narrowed the circumstances of the use of capital punishment, without denying the natural justice satisfied by it, while lifting up evangelical and personalist considerations for ending it. Thus, the text of the Catechism as issued by Pope St. John Paul II, teaches that the circumstances of its use should be reduced to those absolutely necessary for the defense of life.

2267. Assuming that the guilty party's identity and responsibility have been fully determined, the traditional teaching of the Church does not exclude recourse to the death penalty, if this is the only possible way of effectively defending human lives against an unjust aggressor.
If, however, non-lethal means are sufficient to defend and protect people's safety from the aggressor, authority should limit itself to such means, as these are more in keeping with the concrete conditions of the common good and more in conformity with the dignity of the human person.
Today, in fact, as a consequence of the possibilities which the state has for effectively preventing crime, by rendering one who has committed an offense incapable of doing harm - without definitively taking away from him the possibility of redeeming himself - the cases in which the execution of the offender is an absolute necessity ‘are very rare, if not practically non-existent.” (Pope St. John Paul II, Encyclical Evangelium vitae 56)

While the possibility of satisfying the criminological assumptions in the text were then, and now, open to question by people of good will and those of particular expertise in the matter, the Pope’s teaching, nonetheless, amounted to a reading of the signs of the times, setting an objective practical interpretation of the multiple moral principles involved, for the guidance of Catholics.

In the early centuries Christians did not participate in Capital Punishment in imitation of Christ. The imitatio christi was then, as it remains today, the highest standard of holiness. The Christian sought to follow Christ in His virtues, and in His sufferings, even to the point of martyrdom. During the era of persecution, the Christian had little choice, either to take seriously the imitation of Christ, with the likelihood of persecution even martyrdom, or to surrender to the imperial will on some point, even to the point of apostasy. It is unsurprising, therefore, that while recognizing the natural justice of execution as a punishment, Christians did not, during the centuries of Roman persecution, participate in it, either by judging or applying it.

Following the legalization of the faith in 313 A.D., Christians became active in governing, and did begin to rely upon the natural law for the use of just capital punishment, as also of just war. The Fathers did not see this as unfitting in the circumstances, nor that one couldn’t be virtuous while still exercising such offices. Nonetheless, for the clergy the Church has maintained this prohibition down to our times as the evangelical way, for those who exercise the ministry of redemption.

The following quote of St. Ambrose (340 – 397), written to a Christian judge who must try a capital case, both illustrates the acceptance of natural and evangelical considerations in the practices of his day, as well as provides an insight into the Church’s practice in the earlier age of persecution. St. Ambrose holds up mercy over justice in the example of Our Lord and the woman caught in adultery. He concludes his letter as follows,

Letter XXVI. To Studius (c. 360 A.D.). . . .Here is an example for you to follow, for it may be that there is hope of amendment for this guilty person; if he be yet unbaptized, that he may receive remission, if baptized that he may do penance, and offer up his body for Christ. See how many roads there are to salvation!

This is why our ancestors thought it better to be indulgent towards Judges; that by the terror of their sword the madness of crime should be repressed, and no encouragement given to it. For if Communion were denied to Judges, it would seem like a retribution on their punishment of the wicked. Our ancestors wished then that their clemency should proceed from their own free-will and forbearance, rather than from any legal necessity. (St. Ambrose, Letter XXVI. To Studius.)

St. Ambrose Letter XXVI

For all practical purpose, the attitude of the Fathers endured up to our time, sanctioned by the later doctors of the Church, and by the Magisterium. The lack of an intrinsic evil in capital punishment, compared to abortion and euthanasia, for example, distinguishes it from homicide and explains the Church’s differential treatment of these issues. However, the reliance on the natural law, while it can be done virtuously, distinguishes it from the perfect imitation of Christ, whose ministry of mercy is also that of the Church, and whose office of justice He will Himself accomplish at the end of each life, and at the end of the world. The Popes have affirmed in recent decades that while capital punishment is defensible on grounds of temporal justice, it is less and less defensible for Christians on evangelical grounds and on personalist grounds.

In our day, therefore, the Papal Magisterium has increasing laid down the sword in favor of an effective return to the practice of the early Church, with Pope Francis’ changes to the Catechism of the Catholic Church being the firmest teaching of the recent popes. While not declaring capital punishment intrinsically evil, he declares it inadmissible (invalid or not to be tolerated). This makes it, effectively, an act in which all the circumstances and arguments taken together can no longer justify it––even the rare circumstances which Pope St. John Paul II admitted were possible.

The Church continues to otherwise uphold the right to justified and proportionate self-defense of individuals and societies, even resulting in death (cf. CCC 2263-2266)

The Church has never lacked the Scriptures to guide her deliberations, nor her belief in the dignity of the human being, created in the image of God and redeemed by Christ. To this Faith, which is always first in her consideration, she has added theology, which with the assistance of philosophy, seeks to deepen the understanding of the Faith.

As noted above, the early Church took a strongly evangelical approach, unmoderated by other considerations, which only developed over time, and which accompanied the insertion of Christians into civil society. In recent centuries we have seen the almost complete undoing of what came to be considered the Christian West. In a famous lecture in 1958, the future Pope Benedict XVI described this reversal, stating that the Church was no longer,

… composed of pagans who have become Christians, but a Church of pagans, who still call themselves Christians, but actually have become pagans.

Emblematic of this was the 20th Century, the most violent in history, both as a result of warfare, but also in terms of violence motivated by hatred based on political, ethnic, and religious differences. According to the Commission for the New Martyrs of the Great Jubilee, established by Pope St. John Paul II, the number of Christian martyrs alone in the 20th century was double that of all other centuries combined––as high as 26 million.

This violence, largely the fruit of materialist philosophies such as Communism and Nazism, prompted a general philosophical reassessment of the relationship between human beings considered as a thing (a nature), and considered as a person. The resulting philosophical perspective known as Personalism developed between the two World Wars as a reaction to the increasing devaluation of the human person, which continued after WW II down to our day. When the Church and others refer to the increasing sense of the dignity of the person it is referring to this violent history and the reaction to it, which is found among people of many faiths and no faith.

The fruits of personalism, unfortunately, have been decidedly mixed. Outside the Church, and even among some Catholics, it took an existentialist turn, exalting the personal autonomy of the individual (e.g. the prochoice movement), and recently even reducing human sexual nature to a personal choice (e.g. gender ideology). At the other extreme, materialist philosophies persist, in worldviews such as socialism, fascism and some forms of capitalism, aided by the general reduction of human life to a natural life, devoid of moral absolutes--what Pope Benedict XVI called the Dictatorship of Relativism.

The Catholic approach has been different, for being the mean between extremes. The Church recognizes that whatever contribution personalism can make to understanding the human person, it cannot be rightly effected without respecting the authentic knowledge of human nature, which reason can discover and the Church possesses in her perennial philosophy, and it absolutely cannot proceed apart from Divine Revelation and the teaching of the Magisterium. The truths of the latter are guaranteed by something far more certain than human reason, as operative in theology and philosophy, or in the natural and human sciences, they are guaranteed by God revealing and by Christ’s promises to the Church.

On this basis, therefore, the Magisterium has embraced personalism, righty understood and applied, as a handmaid to theology for understanding the human person philosophically, as it did Aristotelianism in the 12th century, as a handmaid to theology for understanding being and nature. The influence of personalism can be seen, therefore, in the documents of the Second Vatican Council and the Papal Magisterium, and especially those of Pope St. John Paul II, whose priestly work as a university and seminary professor in Krakow prior to becoming a bishop, was in this area of ethics.

Finally, many have NOT been persuaded by the arguments that either Pope St. John Paul II made, or Pope Francis makes today in their teaching on capital punishment. In a document promulgated by then Cardinal Ratzinger on The Ecclesial Vocation of the Theologian, the Prefect of the Congregation for the Doctrine of the Faith makes several points, which clarify what ought to be our attitude in such a case. While written for theologians, it is applicable to all believers.

28. . . . a particular application (is) the case of the theologian who might have serious difficulties, for reasons which appear to him well founded, in accepting a non-irreformable magisterial teaching.

Such a disagreement could not be justified if it were based solely upon the fact that the validity of the given teaching is not evident or upon the opinion that the opposite position would be the more probable. Nor, furthermore, would the judgment of the subjective conscience of the theologian justify it because conscience does not constitute an autonomous and exclusive authority for deciding the truth of a doctrine.

29. In any case there should never be a diminishment of that fundamental openness loyally to accept the teaching of the Magisterium as is fitting for every believer by reason of the obedience of faith. The theologian will strive then to understand this teaching in its contents, arguments, and purposes. This will mean an intense and patient reflection on his part and a readiness, if need be, to revise his own opinions and examine the objections which his colleagues might offer him.

On the Ecclesial Vocation of the Theologian