The Bible does not specifically say when life begins. It is clear that life begins before birth, despite some claims to the contrary. Before birth, there are essentially three "bright lines" that can be drawn:
This line is a moving target as technology for supporting very untimely babies improves. The current earliest viability date is around 21-22 weeks from conception. That's significantly earlier than what it would have been about 50 or 100 years ago. In another 50 or 100 years, that age may be pushed back further, perhaps all the way back to conception - we just don't know.
Using viability as a criterion is unsatisfying because of its reliance on technology, and because it means that a baby exactly physically the same but placed 50 years ago or 50 years from now is considered to be alive (or not) differently. Intuitively, most people recognize that this cannot be correct.
A second line that has sometimes been drawn is a line based on what is termed the quickening of the child or what is called the ensoulment of the child. The two are not necessarily exchangeable.
Quickening is sometimes viewed as the first time the child shows signs of life that the mother can detect. This normally occurs around 18-21 weeks, but can occur as early as 14 weeks from conception. Evidently quickening had significance in the English common law, especially as an aggravating circumstance with respect to the homicide of fetal humans.
Ensoulment is the time when an infant's body gains a soul. Certain theologies would actually extend the child's soul indefinitely back to Adam, essentially viewing the soul as being transmitted via the sperm. This would seem to be based at least in part on a defective understanding of Scripture relating to Adam's federal headship.
Sometimes the time of quickening is identified as the time of ensoulment, but Scripture does not specify such a thing.
Quickening is partly counter-intuitive because it basically depends on the sensitivity of the mother. Furthermore, primiparous women usually feel this movement later than multiparous women, which would mean that a physically identical infant that was simply the first to be conceived would gain life later than a corresponding infant that was third to be conceived.
Furthermore, other signs of life are now visible with machine much earlier than when a child begins to kick from within. For example, after only 2 or 3 weeks, a heartbeat can be detected with the right equipment.
One solution is to push back ensoulment to the formation of the heart or brain (around 18 days from conception) or the formation of lungs (slightly later). One issue with such an approach is that there is no compelling Biblical data to suggest one option over another one.
Conception is normally identified as the moment at which a sperm cell and ovum cell combine to form a single diploid cell. This is the most widely accepted (among Christians) date for the beginning of life. There are, however, several objections:
a) Identical Twins
Identical twins are the result of a division of the original diploid cell. If they divide very early, they will have separate placentas. If they divide somewhat later, they will have one placenta with two amniotic sacs. It is believed the conjoined twins divide much later.
Often one objection is that since a given zygote has the biological potential to split after conception, the soul cannot yet be present. In short, the soul cannot be present until after twinning is impossible.
The usual response is either that:
i) the original zygote has two souls (this approach assumes a deterministic view of the world); or
ii) the soul of one of the twins is created upon the splitting (this, in essence, makes one of the twins the ancestor of the other twin).
b) Too Many Deaths
Another argument against the view of life starting at conception is that it results in a large number of deaths, since it is imagines that a significant number of human zygotes fail to embed in the uterus, and consequently die. Additionally, in the production of "test tube babies" a number of zygotes are produced and normally only one or a few is ever introduced into the mother's womb.
This argument mostly appeals to the emotions. If life starts at conception, than infant mortality is much higher than if life starts at birth, but that does not seem to have any rational basis.
c) It's not in the Bible
The Bible does not say that life starts at the moment of conception. The counter-argument here would seem to be that the Bible does speak of people being conceived:
Luke 1:36 And, behold, thy cousin Elisabeth, she hath also conceived a son in her old age: and this is the sixth month with her, who was called barren.
Psalm 51:5 Behold, I was shapen in iniquity; and in sin did my mother conceive me.
Matthew 1:20 But while he thought on these things, behold, the angel of the Lord appeared unto him in a dream, saying, Joseph, thou son of David, fear not to take unto thee Mary thy wife: for that which is conceived in her is of the Holy Ghost.
Luke 2:21 And when eight days were accomplished for the circumcising of the child, his name was called JESUS, which was so named of the angel before he was conceived in the womb.
2 Samuel 11:5 And the woman conceived, and sent and told David, and said, I am with child.
Job 3:3 Let the day perish wherein I was born, and the night in which it was said, There is a man child conceived.
Song of Solomon 3:4 It was but a little that I passed from them, but I found him whom my soul loveth: I held him, and would not let him go, until I had brought him into my mother's house, and into the chamber of her that conceived me.
Hosea 1:6 And she conceived again, and bare a daughter. And God said unto him, Call her name Loruhamah: for I will no more have mercy upon the house of Israel; but I will utterly take them away.
Leviticus 12:2 Speak unto the children of Israel, saying, If a woman have conceived seed, and born a man child: then she shall be unclean seven days; according to the days of the separation for her infirmity shall she be unclean.
Hosea 2:5 For their mother hath played the harlot: she that conceived them hath done shamefully: for she said, I will go after my lovers, that give me my bread and my water, my wool and my flax, mine oil and my drink.
The following essentially make the comment that a woman "conceived (sometimes adding "again"), and bare a son (or the name of the son)"
Genesis 4:1 and 17; Genesis 29:32-35; Genesis 30:5, 7, 17, 19, and 23; Genesis 38:3-5; Exodus 2:2; 1 Samuel 1:20; 1 Samuel 2:21; 2 Kings 4:17; 1 Chronicles 7:23; Isaiah 8:3; and Hosea 1:3 and 8.
The following mention something essentially along the lines of "shall conceive and bear a son"
Judges 13:3, 5, and 7; Isaiah 7:14; and Luke 1:31.
So, the Bible does not explicitly say that conception is when life starts, but it makes a pretty strong connection that way.
Conception is the easiest bright line to use, notwithstanding the objections. Since we have a duty to protect human life, it is preferable to draw the line earlier (perhaps protecting non-life) rather than later (perhaps not protecting life). Birth itself is an absolutely ludicrous standard for the beginning of life, particularly in view of the fact that some children are conceived outside of the body, and the fact that an unborn child can be taken from the womb without the mother giving birth in the conventional sense(Cesarean Section, for example). Furthermore, birth is clearly not the beginning of life according to the Biblical evidence (John the Baptist and Christ being two immediately apparent examples).
There's no particular reason to draw the line before conception, because there is no biological identity of a person before conception. However, the scientific evidence is conclusive that at conception a new biological entity is formed, distinct from both the mother and the father, and remains the same biological entity that is (if all goes well) eventually born.
All in all, therefore, the king (the one who has been given authority by God to rule the nation) has the responsibility of protecting human life including unborn human life. The king, therefore, would be wise to fulfill this responsibility by protecting human life from the moment of conception.
May God persuade the rulers of this earth to do their duty,