Just as you do not know how the lifebreath passes into the limbs
within the womb of the pregnant woman,
so you cannot foresee the actions of God […].
— Koheleth (Ecclesiastes 11.5, Tanakh)
Behind the Hobby Lobby case on one side are two points of doctrine in everyday Christian theology and a question of definition. On another side, there is the conflict over what we Americans want America to be.
The Nicene Creed requires Christians to believe in "the resurrection of the dead and the life of the world to come." So Christians may be "mortalists" and believe that when you're dead you're dead, until the Resurrection and the lifebreath reanimates your body. Most, though — the great majority of Christians and many Abrahamic believers — take real life to be "the life of the world to come" for each individual soul, after death, either with God in heaven or emphatically without God in hell. Body is one thing, and the soul is separable from it and definitely another thing; the mortal body is, at best, the temple of the immortal soul, at worst the soul's prison and a constant temptation to sin and damnation.
For the second point, How is that immortal soul to be saved? Well, "By faith and faith alone," but most Christians believe that our choices, intentions, and desires are important and not merely reflections of whether or not we're saved. Most Christians believe themselves free from the Mosaic Law, but they are really fond of a few of its provisions. Puritans really like the Mosaic rules for sexual purity.
Most serious Christians, then, believe that it's eternal life for the soul that's really important, not the transitory life of the body, and that the salvation of the soul depends on true faith and in following a handful of the 613 Mosaic injunctions, especially those on morality, with "morality" a short form for "sexual morality" (however much Moses and Jesus and the Prophets had a whole lot of other issues in mind).
Now, to say that political decisions about abortion hinge on "when life begins" is ridiculous if by "life" you mean "biological life." Eggs are alive; sperm are alive; and zygotes, embryos, and fetuses are obviously alive. Life does not begin; Bible and biology agree it began, and has been passed on. Considering "when life begins" makes sense, however, if one is talking about human life, or real life: the life of the reborn in Christ, the "life of the world to come." Or the potentially reborn: the life of any creature with a soul.
So, two questions.
First of these two, there's that question of definition, plus a technical distinction and some factual details.
"Birth control" usually involves contraception: preventing the merging of sperm and egg to prevent conception. A "morning-after-pill" or possibly an IUD, however, may prevent not conception but pregnancy, where pregnancy is seen as the implantation of a developing embryo into the uterus and development thereafter. Most birth control methods, then, would be contraception, but some birth control may function as abortifacients, if you define abortion to include anything resulting in the death of a fertilized egg ("zygote") or embryo.
And this returns to the background and foundation for Hobby Lobby issues and much else. In this case: when does the soul enter the child in the womb? One can say that it doesn't: one may not believe in souls, or one may believe the lifebreath is a rather literal breath and comes with the first breath a (now) baby takes. Christians generally believe in a soul more refined than breath, so it can enter the womb earlier. How early? Koheleth, the "Preacher" in the Biblical Book of Ecclesiastes, tosses off as something unknowable how the lifebreath comes to a fetus, so Jews, Christians, and Muslims — peoples of The Book — ought to be cautious in speculating on when it happens. Still, one elegant answer is, At the beginning of individual human life: "ensoulment" occurs at the moment of conception, at the creation of a unique, individual human being (with "monozygotic siblings" — identical twins and such — a limiting case, but not a contradiction).
If zygotes, embryos, and fetuses are ensouled, then abortion is (or at least may be) not only murder but potentially worse than murder. With ensoulment at conception, a fertilized egg is an unbaptized infant, unwashed of Original Sin and — unless saved by a special grace — in big trouble. As God tells "reprobate infants" in Michael Wigglesworth's Day of Doom (1662), however individually sinless they are, these kids are descendants of fallen Adam:
A crime it is, therefore in bliss
you may not hope to dwell;
But unto you I shall allow
the easiest room in Hell. (stanza 181)
Abortion on a large scale, in this argument, is arguably worse than genocide.
A similar argument, if less sensational, can be made with homosexuality.
Since the Fall, sex is at best problematic and needs to be redeemed. The most central method of redemption is to have as sex's goal, reproduction, thereby fulfilling the commandment to both Eve and Adam and Noah to multiply and fill the earth. Plus, a pronatalist policy is good for national defense (as Pharaoh recognized in Exodus) and good for business: "People are the riches of a nation," which isn't exactly Biblical but has a point.
And sex is useful to reinforce the marriage bond between man and woman, established in Eden and reaffirmed by Christ by His attendance at the marriage feast at Cana.
Homosexuality is explicitly forbidden to Jews in what Christians call "The Old Testament," and even if Christians are free of the Law generally, they aren't free of some laws. If our generation can say that homosexuality is OK, how about the other abominations forbidden in Leviticus, such as sex with nonhuman animals? (It's OK though to engage in the abomination of eating shrimp: St. Paul freed Christians from Jewish dietary law — and the rest gets complicated.)
And so forth, including with "the homosexual agenda" the seduction of the young into sin and hence damnation.
Such arguments are logical and elegant. The problem, of course, is that they don't pass (as the cliché has it) Constitutional muster; so we get inelegant arguments, often, in the mouths of politicians talking outside of the religion ghetto, arguments that are intentionally confused and misleading.
So I'd like to hear more from honest Christian Right-wingers who emphatically do want to follow through to the end (reductio ad finem) the logic of their faith, and impose it on America as a Christian nation, not a secular republic. Or, perhaps, it is a proper faith for an America parallel to a restored Caliphate: in our case a renewed Christendom, where no secular law may contradict God's doctrine.
And let's hear more from American small "r" republicans, who don't want imposed upon us a Christian nation or Republic controlled by any of our religions.
But, please, no more bullshit distractions like asking "When life begins." Yet again, it began. There are technical questions about how IUD's work and other recent methods of birth control, but let's just start with allowing "There's always a death in an abortion" even as there are over 100 million little deaths with every human male ejaculation and at least one dead egg with each menstruation and many, many zygotes and young embryos not getting implanted and getting, so to speak, flushed out to die. One serious question is what dies and how much legal protection to give it/him/her, if any. Another serious question is what extent beliefs on such basic issues should be applied to public policy. A third serious question adds to "What are they" the equally contested issue of "Who are we?"
I'm a citizen of the American Republic, and not part of a Christian nation. I kind of like the idea of "lifebreath," but as a figure of speech, not a theory for how (land) animals function. I don't think I'd get far in an argument with a logically-consistent Christian, let's say a devout Jesuit. But I think we everyday American can work out compromises that are logically incoherent and maybe philosophically disreputable — but that allow policies that are respectful, compassionate, roughly just, and practical.
Someplace along the line, an embryo becomes a human being; we can recognize that, and respect the rights of women to control their bodies, and the rights of citizens generally to be left the hell alone ordinarily, and given help when its good policy to do so.
If we argue sensibly enough, we may even get health care for all Americans and can start to work on population policy, immigration, preserving resources, rebuilding infrastructure, ameliorating climate change, nuclear-weapons reduction: well, the wonkish issues we ignore to get to round 457 of our much figuratively sexier Culture Wars over sex.