Two important terms in theology are “nature” and “person.” Both terms help us understand the central Christian doctrines of the Trinity and the Incarnation. With regard to the Trinity, we have one nature and three persons. God is three “who’s” but one “what”. The three persons share the same nature, so that all three are fully God, and yet there is only one God. With regard to the Incarnation, Jesus Christ is one person with two natures. He is one “who” with two “what’s,” one person who is both fully divine and fully human. Both of these truths are great mysteries, because in our experience singular personhood is always tied to an individual human nature. We have nothing analogous to the Trinity or to the Incarnation in normal experience, so we bow before the mystery.
The word “person” has also been an important one in ethical debates about human life. With regard to the issue of abortion, many on the pro-choice side have argued that, prior to a certain point (usually birth, viability outside the womb, or some standard of functionality), a fetus is not a human person. It is certainly a living being of some sort, but personhood has not been established (so the argument goes) until some particular point of development. The logical result of this argument is that abortion prior to the establishment of the fetus’s personhood is morally acceptable, for it does not constitute murder. To kill the fetus is not to kill a person, so the act of abortion may be considered ethically analogous to putting a pet to sleep, a practice that is widely accepted as ethical in our society. Much of the debate over abortion centers on the question of the moral status of the fetus. Is it a person or not?
My contention is that the Christian doctrine of the Incarnation helps to establish the personhood of all fetuses; therefore, all Christians should regard abortion as an immoral practice, the taking of life from an innocent human person. Here is how my thinking goes on this. Jesus Christ is one person with two natures. The church has long confessed that the personhood of Christ does not come from his human nature; the person of Christ is the eternal Word, the divine Son, the second person of the Trinity. The human nature of Christ has no personhood of its own; it is personalized by the Word. The Word did not unite himself to a personalized human nature, an individual person known as “Jesus of Nazareth.” That view is a heresy known as “Nestorianism,” the view that Jesus Christ is basically two people, a fully human person alongside a fully divine person. In order to maintain that Christ is one person uniting two complete natures (known as the “hypostatic union”), we must say that the one person of Christ is in no way derived from his human nature. The divine Word, who is eternally a personal being, simply added to himself a human nature and thereby personalized that nature. The human nature of Christ is a personal nature, but its personhood comes from outside itself. In this way, Jesus Christ is one person with two natures.
But when did the eternal, divine Word personalize Christ’s human nature? It had to be at the very instant that the Word united himself to the human nature. In other words, from the moment the human nature of Christ was united to the Word, it was a personal human nature. Jesus Christ was a human person from that moment on. When did that happen? It happened at the moment the human nature of Christ was formed as an embryo in the womb of Mary. The human nature of Christ has no existence apart from the personhood of the divine Word. Therefore, there was never a time that one could say that Christ’s human nature was not a person. From (miraculous) conception on, Mary had a fully human person in her belly.
Now, let’s work from the Incarnation to human life in general. Does human nature ever exist apart from personhood? Even though the Incarnation is a unique event, we can still draw the conclusion that personhood and human nature go together. If a human nature exists within the womb of a woman at any stage of development, we have no theological warrant to de-personalize it and kill it. That Jesus Christ was a person even in the embryonic stage indicates that personhood does not depend on a certain level of human development or functionality. Any living being with a human nature constitutes a human person. Personhood is an ontological category, not a functional one. Therefore, to take the life of an unborn baby constitutes taking the innocent life of a human person. Embryos and fetuses are not essentially different from the rest of us. They are merely human beings (with the ethical status of personhood) at an early stage of development.