What does the Catholic Church teach about abortion, and why?

The teaching. "Human life must be respected and protected absolutely from the moment of conception" (CCC 2270). "Direct abortion, that is to say, abortion willed either as an end or a means, is gravely contrary to the moral law" (CCC 2271). This has been the constant teaching from the first century: the Didache (c. 70 AD) says, "You shall not murder a child by abortion."

Why. A new human being with unique DNA exists from fertilization; that is biology, not theology. Faith adds that every human being is made in God's image (Gen 1:27), known by Him before birth ("Before I formed you in the womb I knew you," Jer 1:5), and redeemed by Christ. John the Baptist leapt in the womb at the presence of the unborn Jesus (Lk 1:41). The Church cannot accept that some human beings may be killed for the benefit of others. St. John Paul II taught in Evangelium Vitae 62 that this teaching is unchangeable.

Hard cases. The Church grieves with women in crisis and works to provide the alternatives that make abortion unnecessary; Catholic organizations are the largest private providers of such help. Treatments that save the mother's life and indirectly cause the child's death (ectopic pregnancy, cancer) can be morally permissible under the principle of double effect; direct killing is not. Pregnancy from rape is a terrible injustice, but the child is innocent of it.

Mercy. Abortion carries automatic excommunication under canon law (Canon 1398), which signals its gravity, but every priest may now lift it in confession. Pope Francis said that God's mercy is unlimited and urged those who have had abortions to come to confession without fear. Ministries like Project Rachel exist for exactly this healing. There is no sin here that cannot be forgiven, and no one the Church wants to turn away.