Almost everyone has heard of the Ten Commandments, and many can name at least three or four; in fact, there must be a good few million who can list all ten, in order. Less common, however, is the knowledge that this 10-point encapsulation of G‑d's message to man reads in two directions: from top to bottom, and from side to side.
What do I mean? The Ten Commandments were given to Moses engraved on two stone tablets -- five commandments on each stone -- like this:
1) I am the L‑rd your G‑d...
2) You shall have no other gods...
3) Do not take G‑d's name in vain...
4) Remember the Shabbat...
5) Honor your father and your mother...
6) Do not kill
7) Do not commit adultery
8) Do not steal
9) Do not bear false witness...
10) Do not covet... anything of your fellow's
Why on two tablets? And why are the first five Commandments on one stone and the second five on the other? (5/5 may seem an even division, but it's really not: the first five Commandments total 146 words in the original Hebrew, the second five 26.) One of the reasons given by our sages is that the five latter Commandments are actually a reiteration of the first five. In other words, we're supposed to place these two tablets side by side and read across, like this:
1) I am the L‑rd your G‑d / Do not kill
2) You shall have no other gods / Do not commit adultery
3) Do not take G‑d's name in vain / Do not steal
4) Remember the Shabbat / Do not bear false witness
5) Honor your father and your mother / Do not covet anything of your fellow's
This means that, in essence, there are only five Commandments. "Do not kill" is another way of saying "I am the L‑rd your G‑d"; the prohibition against adultery is the prohibition against idolatry; keeping Shabbat means being a truthful witness; and so on.
The Midrash explains the correlations of each of these five sets, but for starters, we'll look at the connection between Commandments #1 and #6. Why is "Do not kill" the flip side of "I am the L‑rd your G‑d"? Because, say the Sages, to murder a fellow man is to murder G‑d:
What is this analogous to? To a king of flesh and blood who entered a country and put up portraits of himself, and made statues of himself, and minted coins with his image. After a while, the people of the country overturned his portraits, broke his statues and invalidated his coins, thereby reducing the image of the king. So, too, one who sheds blood reduces the image of the King, as it is written (Genesis 9:6): "One who spills a man's blood... for in the image of G‑d He made man."
Now there are murderers who say they believe in G‑d. And there are people who are dead-set against murder who claim not to believe in a higher power. They're both wrong.
If you truly believe in G‑d, you are incapable of murder. And if you truly believe that taking the life of another human is wrong -- not just because you lack the means or motive to do so or are afraid of ending up in jail, but because you recognize the transcendent, inviolable value of life -- that's just another way of saying you believe in G‑d. Even if you're not one of those religious types who put it in those terms.