There are plenty of famous lines in the bible, from the ten commandments to the four horsemen. One of the best-known lines in the whole book though is Exodus 22:18, which in the King James version of the bible (the one all those Gideons keep putting in hotel rooms) reads "Thou shalt not suffer a witch to live." It seems pretty straightforward, but there's a lot more going on behind this phrase than you know. In fact this line, which has been the source of problems from African witch hunts to inter-faith conflicts between Christians and neo-pagan faiths, might actually be the result of a particularly poor translation.
Also, have you ever wondered what angels really look like (according to the bible)?
We're Not Actually Sure The Word Is "Witch"
The first thing that people tend to forget when this quote comes up is that language changes with time and culture. The word witch means a lot of different things today, ranging from child-eating monsters in fairy tales to characters in fantasy novels to practitioners of Earth-based faiths. It's an English word though, and it doesn't really have a twin when it comes to the languages and dialects that were spoken in the Middle East at the time Exodus was being put down on scrolls. There was certainly no such thing as modern ritual magic or new age faiths like Wicca. So saying that this book which was written more than a thousand years ago is referring to cultural constructs that we have today which simply didn't exist at the time is ridiculous.
Even keeping that this quote comes from another time and another world in mind though, witch might still be an inappropriate term. While the quote from the KJV is the most famous there are a slew of different translations which alter the word to sorceress (which might be a more accurate term, as you'll see if you read about the history of the word sorcerer), or which imply that anyone who uses magic should be put to death. For these latter there is no distinction made between the casting of genuine spells and stage magic. These are all problematic though because there really is no English language translation for the term that appeared in the original scripture; m'khashepah.
There really isn't a good word for what this term means, but the closest understanding seems to be "a woman who uses spoken spells to harm others." English isn't really good at being specific with just one word, but taken at a glance witch doesn't seem to be a totally inaccurate stand-in. At least until you look at...
A More-Accurate Translation Might Actually Be "Poisoner"
Language can take some funny turns, as you well know if you've ever tried to have a conversation with a foreign pen pal using nothing more than Google translate. Given that the bible has been put through a dozen translations between ancient Hebrew and English it's really no surprise that what started off as one term can easily grow and change into another.
How does that apply to Exodus 22:18? Well for that we need to take a glance at Revelation 21:8.
This passage in Revelation originally contained the Greek word pharmakous, which could mean magician but which could just as easily refer to a mixer of poisons. The New Testament was originally written in Greek, which may have led to the old one being translated. The problem is that there's no way to know whether or not the definition was meant to be more mystical or more mundane. It's unlikely that witches curdling milk was a serious threat even in the olden days, but it's possible that the use of poison was something that would have been harshly punished.
More Than Meets The Eye
Religious texts are often thought of as places for clear, simple guidance on complex living. It's important to remember that even biblical scholars and archaeologists who have spent their lives dedicated to the ancient world that created this book are occasionally at a loss for what particular passages truly mean. If you add in the very natural translation errors in both language and culture, combined with royal and organizational decrees such as those handed down by King James while the KJV was being re-written, and it's no wonder that even simple phrases may very well mean something else completely.