I. Respect for human life 
Human life is sacred because since its inception it is the fruit of the creative action of God and always remains in a special relationship with the creator, his only purpose. 

By: Catechism of the Catholic Church | Source: Part Three: Life in Christ 

THIRD PART
LIFE IN CHRIST 
SECOND SECTION 
THE TEN COMMANDMENTS

CHAPTER TWO
"LOVE YOUR NEIGHBOR AS YOURSELF" 

ARTICLE 5 
THE FIFTH COMMANDMENT

You will not kill (Ex 20, 13). 

You have heard that the ancestors were said: Thou shalt not slay, and who kills will be convicted in court. For I say unto you, whosoever shall be anger against his brother shall be inmate before the court (Mt 5, 21-22). 

2258 Human life is sacred because since its inception it is the fruit of the creative action of God and always remains in a special relationship with the Creator, his only purpose. Only God is the Lord of life from his beginning to his term; no one, under any circumstances, can be attributed the right to directly kill an innocent human being (CDF, InStr. "Donum vitae" intr. 5). 

I. The respect for human life 

2259 The Scripture, in the story of Abel's death at the hands of his brother Cain (cf Gn 4, 8-12), reveals, from the beginnings of human history, the presence in man of wrath and greed, consequences of original sin. The man became the enemy of his fellow men. God manifests the wickedness of this fratricide: What have you done? You hear your brother's blood cry out to me from the ground. Well, damn you, away from this floor that opened his mouth to receive from your hand the blood of your brother (Gn 4, 10-11). 

2260 The covenant of God and humanity is woven of calls to recognize human life as a divine gift and of the existence of fratricidal violence in the heart of man: And I promise to reclaim your blood... Who poured the blood of man, by another man shall be his blood poured out because in the image of God He made the man (Gn 9, 5-6). 

The Old Testament always considered blood as a sacred sign of life (cf Lv 17, 14). The validity of this teaching is for all time. 

2261 The Scripture specifies what the fifth commandment forbids: Do not take away the life of the Innocent and righteous (Ex 23, 7). The willful killing of an innocent man is gravely contrary to the dignity of the human being, to the golden rule and the holiness of the Creator. The law that outlaws it has a universal validity: it obliges each and everyone, always and everywhere. 

2262 In the Sermon on the Mountain, the Lord recalls the precept: Thou shalt not slay (Mt 5, 21), and add the absolute rejection of wrath, hatred, and vengeance. Moreover, Christ demands his disciples to present the other cheek (cf Mt 5, 22-39), to love the enemies (cf Mt 5, 44). He did not defend himself and told Peter to keep his sword in the sheath (cf Mt 26, 52). 

The legitimate defense

2263 The self-defense of individuals and societies is no exception to the prohibition of the death of the innocent that constitutes voluntary homicide. “The action of defending oneself can entail a twofold effect: one is the preservation of life itself; the other, the death of the aggressor... only one is dear; the other, no' (S. Thomas Aquinas, S. Th. 2-2, 64, 7). 

2264 Love itself constitutes a fundamental principle of morality. It is therefore legitimate to enforce the right to life. He who defends his life is not guilty of murder, even when he is forced to attack his aggressor with a deadly blow: if to defend oneself there is greater violence than necessary, it would be an illicit action. But if violence is rejected in a measured way, the action would be lawful... and it is not necessary for salvation to omit this act of measured protection in order to avoid killing the other, because it is greater the obligation that one has to watch over one's own life than that of another (S . Tomás de Aquino, S. Th. 2-2, 64, 7). 

2265 Self-defense can be not only a right but a serious duty, for the one who is responsible for the life of another, the common good of the family or society." 

2266 The preservation of the common good of society requires that the aggressor be placed in a state of no harm. For this reason, the traditional teaching of the Church has recognized the right and duty of the legitimate public authority to apply penalties proportionate to the seriousness of the crime, without excluding, in cases of extreme severity, the recourse to the death penalty. For similar reasons, those who possess the authority have the right to refuse by means of arms to the aggressors of the society they are responsible for. 

Penalties have the first effect of compensating for the disorder introduced by the fault. When the penalty is voluntarily accepted by the culprit, it has a value of atonement. The penalty also has the effect of preserving public order and the security of people. Finally, it also has medicinal value, since it must, as far as possible, contribute to the amendment of the culprit (cf Lc 23, 40-43). 

2267 If the means bloodless enough to defend the human lives against the aggressor and to protect from him the public order and the security of the people, in that case the authority will limit itself to employ only those means, because they correspond better to the conditions of the common good and are more compliant with the dignity of the human person. 

Voluntary homicide 
2268 The fifth commandment condemns as gravely sinful the direct and voluntary murder. He who kills and those who voluntarily cooperate with him commit a sin that cries out for vengeance to heaven (cf Gn 4, 10). 

Infanticide (cf GS 51, 3), fratricide, parricide, homicide of the spouse are especially serious crimes because of the natural links they destroy. Eugenics or public health concerns cannot justify any homicide, even if ordered by the authorities themselves. 

2269 The fifth commandment prohibits doing something to indirectly provoke the death of a person. The moral law prohibits exposing someone without a serious reason to a deadly risk, as well as denying assistance to a person in distress. 

The acceptance by the society of hunger that causes deaths without striving to remedy them is a scandalous injustice and a serious foul. Traffickers whose usury and mercantile practices provoke the hunger and death of their brothers, men, indirectly commit murder. This is attributable to them (cf Am 8, 4-10). 

Involuntary homicide is not morally imputable. But it is not free from serious failure when, without reasons provided, it has been done in a way that has been followed by death, even without intent to cause it. 

The abortion 
2270 Human life must be respected and protected in an absolute way from the moment of conception. From the first moment of its existence, the human being must-see recognized his rights of the person, among which is the inviolable right of all being innocent to the life (cf CDF, InStr. "Donum vitae" 1, 1). 

Before I formed you in the womb, I knew you, and before you were born I had you consecrated (Jr 1, 5; Jb 10, 8-12; Sal 22, 10-11). 
And my bones were not hidden from you, when I was made in the secret, woven in the deepness of the earth (Sal 139, 15). 

2271 Since the first century, the Church has affirmed the moral malice of all provoked abortion. This teaching has not changed; remains unchanged. Direct abortion, i.e., wanted as an end or as a means, is gravely contrary to the moral law. 

You will not kill the embryo by means of abortion, you shall not die to the newborn. (Didajé, 2, 2; Bernabé, Ep. 19, 5; Epistle to Diognetus 5, 5; Tertuliano, apol. 9).

God, Lord of Life, has entrusted to men the lofty mission of conserving life, a mission that must be fulfilled in a dignified manner to man. Therefore, life must be protected with the utmost care from conception; both abortion and infanticide are abominable crimes (GS 51, 3). 
2272 Formal cooperation in an abortion constitutes a serious foul. The Church sanctions with the canonical penalty of ex-communication this offense against human life. 'Who seeks abortion, if it occurs, incurred in ex-communication latae sententiae' (CIC can. 1398), that is to say, 'so that it ipso facto incurs in it who commits the crime' (CIC can. 1314), under the conditions envisaged by the law (cf CIC can. 1323-1324). With this, the Church does not intend to restrict the scope of mercy; what it does is manifest the seriousness of the crime committed, the irreparable damage caused to the innocent to whom death is given, to his parents and the whole society. 

2273 The inalienable right of every innocent human individual to life constitutes a constituent element of civil society and its legislation: 
'The person's inalienable rights must be recognized and respected by civil society and political authority. These rights of man are not subordinate either to individuals or to parents, nor are they a concession of society or State: they belong to human nature and are inherent to the person by virtue of the creative act that has originated it. Among these fundamental rights, it is necessary to remember to this purpose the right of every human being to life and physical integrity from conception to death ' (CDF, InStr. "Donum vitae" 3). 

'When a positive law deprives a category of human beings of the protection that the civil order owes them, the State denies the equality of all before the law. When the State does not put its power at the service of the rights of every citizen, and particularly those who are weaker, the very foundations of the rule of law are broken... The respect and protection that must be guaranteed, from the very conception to the one to be born, requires that the law provides for appropriate penal sanctions for any deliberate violation of its rights'. (CDF, InStr. "Donum vitae" 3). 

2274 Since it must be treated as a person from conception, the embryo must be defended in its entirety, cared for and cared for medically as far as possible, like any other human being. 

Prenatal diagnosis is morally lawful, 'if it respects the life and integrity of the embryo and the human fetus, and whether it is directed towards its protection or its healing... But it will seriously oppose the moral law when it contemplates the possibility, depending on its results, to provoke an abortion: a diagnosis attesting to the existence of a malformation or a hereditary disease should not amount to a death sentence' ( CDF, InStr. "Donum vitae" 1, 2). 

2275 The interventions on the human embryo should be considered 'lawful, provided that they respect the life and integrity of the embryo, that they do not expose it to disproportionate risks, that they have the purpose of their healing, the improvement of their health conditions or their survival Individual ' (CDF, InStr. "Donum vitae" 1, 3). 

'It is immoral to produce human embryos destined to be exploited as 'biological material' available' (CDF, InStr. "Donum vitae" 1, 5). 
'Some attempts to intervene in chromosomal and genetic heritage are not therapeutic, but they look to the production of selected human beings in terms of sex or other prefixed qualities. These manipulations are contrary to the personal dignity of the human being, his integrity and his identity ' (CDF, InStr. "Donum vitae" 1, 6). 

Euthanasia 
2276 Those whose life is diminished or weakened has the right to special respect. People who are sick or diminished should be taken care of to live as normal as possible. 

2277 Whatever the motives and means, direct euthanasia consists of ending the lives of people who are diminished, sick or dying. It's morally unacceptable. 

Therefore, action or omission that, in his or her intention, causes death to suppress pain, constitutes a homicide gravely contrary to the dignity of the human person and the respect of the living God, his creator. The error of judgment in which it may have fallen in good faith does not change the nature of this homicidal act, which must always be rejected and excluded.

2278 The interruption of onerous, dangerous, extraordinary or disproportionate medical treatment to the results may be legitimate. To interrupt these treatments is to reject the therapeutic fiercely. This is not intended to cause death; it is accepted not to be able to prevent it. The decisions must be made by the patient, if for this he has competence and capacity or if not for those who have the legal rights, always respecting the reasonable will and the legitimate interests of the patient. 
2279 Although death is deemed imminent, ordinary care due to a sick person may not be lawfully interrupted. The use of analgesics to alleviate the sufferings of the dying, even at the risk of shortening their days, can be morally according to human dignity if death is not intended, neither as an end nor as a means, but only foreseen and tolerated as inevitable. Palliative care constitutes a privileged form of selfless charity. For this reason, they must be encouraged. 

The suicide 
2280 Each is responsible for his life before God who has given it to him. He's still his sovereign master. We are obliged to receive it with gratitude and to preserve it for your honor and the salvation of our souls. We are administrators and not owners of the life that God has entrusted to us. We don't have it. 

2281 Suicide contradicts the natural inclination of the human being to preserve and perpetuate his life. It is gravely contrary to the just love of itself. It also offends the love of others because it unfairly breaks the bonds of solidarity with the family, national and human societies with which we are obliged. Suicide is contrary to the love of the living God. 

2282 If it is committed with an intention to serve as an example, especially for young people, suicide also gains the seriousness of the scandal. Voluntary cooperation with suicide is contrary to the moral law. 

Serious psychic disorders, distress, or serious fear of testing, suffering, or torture may lessen the responsibility of the suicidal. 

2283 It must not be despaired of the eternal salvation of those who have died. God may have facilitated them by ways that he only knows the occasion of savior repentance. The Church prays for the people who have made an attempt on their lives.