The Bible is not a scientific treatise on biology, reproduction, or anything else
It seems an obvious statement, except, based on the number of times I hear Bible verses, cherry picked of course, thrown out in abortion debates, it apparently isn't. So let me say it. The Bible is not a treatise on biology. It's a book of song, of poetry, of law, of story, even of the first recorded instances of men reproducing without female involvement (“and he begat a son who begat another son who begat another son”)...what it does not contain, however, is a study of the biological aspects of human reproduction.
“But...but it says God knew me in the womb! It says God wove me together! That means that I was a person from the instant sperm met egg! Which obviously means that abortion is murder!”
No, on all counts but one. Those verses exist, yes, but they are not – as context makes very clear – intended to be scientific commentary or an actual representation of the biological processes involved, anymore than the phrase “before you were a glint in your father's eye” is.
Let's start with Psalms 139:13-14. The New American Standard reads:
“13 For You formed my inward parts;
You wove me in my mother’s womb.
14 I will give thanks to You, for I am fearfully and wonderfully made;”
That's the part that you'll see quoted, a lot. But that's only a verse and a half. Let's keep reading (emphasis added):
“Wonderful are Your works,
And my soul knows it very well.
15 My frame was not hidden from You,
When I was made in secret,
And skillfully wrought in the depths of the earth;
16 Your eyes have seen my unformed substance;
And in Your book were all written
The days that were ordained for me,
When as yet there was not one of them.”
All of a sudden, that seems far less, “Oh my gosh, God is hand-crafting kids and every abortion is destroying God's handiwork!” and more creepy, “Keebler-elf” kid factory. At least, that's the mental image that my weird mind conjured up. (For curiosity's sake, verse 15 in the King James reads, “My substance was not hid from thee, when I was made in secret, and curiously wrought in the lowest parts of the earth.” I do love the KJV...everything sounds so much more intense and interesting there...). At any rate, you will often see the “formed my inward parts”/”fearfully and wonderfully made” lines, but you will never see it used in conjunction with the continued sentiment. Why? Because the poetic license the author uses throughout becomes increasingly more clear if you read the very next verse. It's going to be hard to convince the faithful that every embryo is a handcrafted Jesus Original© if you bring up the underground baby factory.
Then there's Jeremiah 1:5: “Before I formed thee in the belly I knew thee; and before thou camest forth out of the womb I sanctified thee, and I ordained thee a prophet unto the nations.”
This is the chapter detailing the calling of the prophet Jeremiah, where God explains how and why he has chosen him. While the good Lord uses some figurative language in these descriptions (verse 18, for instance: “For, behold, I have made thee this day a defenced city, and an iron pillar, and brasen walls against the whole land, against the kings of Judah, against the princes thereof, against the priests thereof, and against the people of the land”), it's that verse in particular upon which people focus their literal interpretations. No one, for obvious reasons, suggests that God actually made Jeremiah a city, a pillar and walls; but they accept the literal reading of the other verse, the one that suits the pro-life argument, without question. God handcrafted Jeremiah the Fetus, because a literal reading of verse five says so; but did he handcraft Jeremiah the City, Jeremiah the Walls, or Jeremiah the Iron Pillar as a literal reading of verse eighteen suggests? That's just being silly.
This is, perhaps, the strongest verse the anti-abortion crowd quotes (simply because there's nothing in the next sentence to show that it absolutely, without a doubt, shouldn't be interpreted literally) -- and there's nothing beyond wishful thinking to indicate that it's anything more than figurative. In fact, there's nothing beyond wishful thinking to indicate that verse eighteen should be read as “you're going to be the defense of my people” but five should be read as anything other than, “since I know everything, including the fact that you'd be born, I've long planned for you to be my people's defender.” But there's plenty of wishful thinking out there...
There's another, perhaps more obvious, side to this though. The Christian pro-life movement is eager to seize upon any verse that might, if read in the necessary way, anthropomorphize a fertilized egg. But what about those verses that suggest that the Jesus Original©, full fledged (albeit single celled) human being starts before it's a fertilized egg? What about, say, Hebrews 7:10, which lends “personhood” to a sperm: “For he was yet in the loins of his father, when Melchisedec met him”? The silence, particularly from the Protestant pro-lifers, is deafening.
Why? Again, it doesn't further the argument to acknowledge those statements. The “glint in his father's eye”-type references only matter, and are only quoted, when they can be interpreted in a fashion that furthers the idea that every zygote, every embryo, and every fetus is a Jesus Original© baby. Therefore God's in-the-womb construction must be quoted, but the next-breath underground-baby-factory is ignored; God's choice of flowery language is to be interpreted literally as it references Jeremiah in the womb, but figuratively outside; and we just won't mention the anthropomorphic sperm that Melchisedec “met”.
This is the problem with trying to glean scientific truths from cherry-picked, half-quoted bits of ancient text: it doesn't hold up to scrutiny. If this is the crux of your argument, you will have no argument after a few minutes of intellectually honest examination. Snippets of select verses might make nice sound bites and look good splashed across cherub-faced-baby-memes, but they make shallow and intellectually lazy arguments. Ultimately, the Bible is not, and should not be treated as, a scientific treatise. It's just that simple.