It can seem like the Catholic Church today, particularly in the United States, is very focused on abortion and that this focus is a recent thing. This is probably because the problem of abortion is very relevant and common in today's world so the Church sees the need to focus attention on it to bring about its end. However, the Church has always taught that abortion is wrong, even from its earliest days. The Bible has several passages which condemn the killing of innocent children, and the early church fathers also spoke against this.
In the Bible
In the book of Jeremiah, God speaks of the care and love he has for the unborn. "Now the word of the Lord came to me saying, 'Before I formed you in the womb I knew you, and before you were born I consecrated you; I appointed you a prophet to the nations.'" - Jeremiah 1: 4 – 5. In the Psalms, the psalmist prays to God and thanks Him for keeping him safe even before his birth. "For thou didst form my inward parts, thou didst knit me together in my mother's womb. I praise thee, for thou art fearful and wonderful. Wonderful are thy works! Thou knowest me right well; my frame was not hidden from thee, when I was being made in secret, intricately wrought in the depths of the earth." - Psalms 139: 13 – 15. These old testament passages demonstrate that the unborn are persons and are cared for by God. Even before their birth, they are part of God's plan and He makes sure that they are safe.
In the New Testament, John the Baptist bears witness to the life of the unborn. "When Elizabeth heard Mary's greeting, the child leaped in her womb. And Elizabeth was filled with the Holy Spirit and exclaimed with a loud cry, 'Blessed are you among women, and blessed is the fruit of your womb. And why has this happened to me, that the mother of my Lord comes to me? For as soon as I heard the sound of your greeting, the child in my womb leaped for joy.'" - Luke 1: 41 – 44. At this meeting of Mary and Elizabeth, John the Baptist, an unborn baby in Elizabeth's womb, leaps to show his joy at the coming of Mary and the unborn Jesus. This is the action of a child, of a person.
Early Church Fathers
Not only does the Bible speak as to the humanity of unborn babies, but the early fathers of the church, from the first several centuries AD, speak against abortion.
"In our case, murder being once for all forbidden, we may not destroy even the fetus in the womb, while as yet the human being derives blood from other parts of the body for its sustenance. To hinder a birth is merely a speedier man-killing; nor does it matter whether you take away a life that is born, or destroy one that is coming to the birth. That is a man which is going to be one; you have the fruit already in the seed." - Tertullian Apologia 9.8
"Women who were reputed to be believers began to take drugs to render themselves sterile, and to bind themselves tightly so as to expel what was being conceived, since they would not, on account of relatives and excess wealth, want to have a child by a slave or by any insignificant person. See, then, into what great impiety that lawless one has proceeded, by teaching adultery and murder at the same time!" - Hippolytus Refutation of All Heresies 7.8.4
The womb of his wife was smitten by a blow of his heel; and in the miscarriage that soon followed, the offspring was brought forth, the fruit of a father’s murder. And now he dares to condemn the hands of those who sacrifice, when he himself is more guilty in his feet, by which the son, who was about to be born, was slain? - Cyprian Epistle 48
Let her that procures abortion undergo ten years' penance, whether the embryo were perfectly formed, or not. - Basil the Great First Canonical Letter Canon 2
What cause is there for the exposure of a child? The man who did not desire to beget children had no right to marry at all. He certainly does not have the right to become the murderer of his children, because of licentious indulgence. - Clement of Alexandria Stromata 2.18
Sometimes, indeed, this lustful cruelty, or if you please, cruel lust, resorts to such extravagant methods as to use poisonous drugs to secure barrenness; or else, if unsuccessful in this, to destroy the conceived seed by some means previous to birth, preferring that its offspring should rather perish than receive vitality; or if it was advancing to life within the womb, should be slain before it was born. - Augustine De Nube et Concupiscentia 1.17
These passages bear witness to the ancient condemnation of killing the unborn. These revered Church Fathers all speak against this practice which was all too common even in those ancient days. The Roman Empire had laws protecting people who wanted to kill their unborn or newly born children, and yet these Catholic authors were willing to go against the common opinion to proclaim the truth that killing the unborn is indeed murder.
