Christians most often cite two scriptures when tackling abortion:
Jeremiah 1:5 - "Before I formed you in the womb I knew you, before you were born I set you apart"
Psalm 139:16 - "Your eyes saw my unformed body. All the days ordained for me were written in Your book before one of them came to be."
These scriptures certainly speak clearly on the issue of God valuing and treasuring each of us, even before birth. They reflect the marvelous quality of God's handiwork, even before science knew exactly how detailed, complex, and sophisticated the fetus was. By eight weeks -- the time most abortions are performed -- every organ system is present in the fetus. The bones are formed, the hands and feet, kidneys and adrenal grands, eyes and ears and brain. The unborn child is God's handiwork, a masterpiece in progress. The scriptures recognize this.
Another scriptural reference to unborn life is the wrestling in the womb of Esau and Jacob within Rebekah's body (Genesis 25:21-23):
Isaac prayed to the Lord on behalf of his wife, because she was barren. The Lord answered his prayer, and his wife Rebekah became pregnant. The babies jostled each other within her, and she said, "Why is this happening to me?" So she went to inquire of the Lord. The Lord said to her, "Two nations are in your womb, and two peoples from within you will be separated; one people will be stronger than the other, and the older will serve the younger." (NIV)
Of course, this scriptural passage was written long before ultrasound allowed us to observe behavior in the womb. But it turns out that twins do indeed wrestle in the womb, do touch and interact with one another. And God uses this normal human behavior, and Rebakah's unusal recognition of this behavior, to reveal the future of her descendants to Rebekah.
Perhaps the most famous act by a fetus in the Bible is the leaping of John the Baptist within Elizabeth's womb at the sound of her cousin Mary's voice (Luke 1:41-44):
When Elizabeth heard Mary's greeting, the baby leaped in her womb, and Elizabeth was filled with the Holy Spirit. In a loud voice she exclaimed: "Blessed are you among women, and blessed is the child you will bear! But why am I so favored, that the mother of my Lord should come to me? As soon as the sound of your greeting reached my ears, the baby in my womb leaped for joy. (NIV)
As John the Baptist was later to announce the coming of the Messiah to the multitudes as a man, he announced the Incarnation to his mother while still in the womb. His destiny was already in motion, and the Spirit of God already active in him, directing him, even before his birth.
If we search the Bible for signs of when God first begins to love each of us, we see that His love is eternal -- that it precedes our existence. But how are we, who live within the limitations of time, to live out that love to one another? We can not act in love toward those who, from within our prison of time, do not yet exist, except to be prepared to welcome our fellows when they arrive in this finite world, to live out their lives among us. To countenance abortion even in theory is to prepare to reject those who God holds in His mind, who He already loves with His perfect love. And to practice abortion in reality is to reject our brothers and sisters, in a very real and concrete way, by killing them. In doing so, we sin not only against our brothers and sisters by breaking the Commandment against murder; we sin against Christ by killing Him in them, for as we do to them, we do to Him.