Do not allow a sorceress/witch to live?

Under the old testament law then that is what God commanded, yes; but Christ is the fulfillment of the law. The law was a tutor to bring us to christ. The law is not so much finished as fulfilled. When the pharisees brought a woman caught in adultery to jesus. He said .... "fine, stone her then, in accordance with the law just let one who has committed no sin throw the first stone". Christ teaches that while technically all sin should be punished yet there is no one worthy of wielding the whip but a sinless one ..... and that single sinless one ( jesus ) doesnt condem us, and so we are in a new revelation, a new testament, the church age, the age of grace, not under condemnation. There will come a day when every bit of evil will be punished, when the lord returns with a sword but meanwhile, no, he doesnt expect us ( or even allow us ) to exact punishment on the breaking of old testament laws which were for a previous generation. Read the book of romans for more information on this particularly chapters 6 to 8. This is a HUGE subject requiring a lot of study to understand, in essence it is a large part of the core of the gospel, but it does make an awful lot of sense and in retrospect it's actually quite simple, just that we are conditioned in this world to sin righteousness, judgement and the like and not to grace, which is an entirely different animal.

You can reference To what extent does the Law of Moses still apply? to help determine if Exodus 22:18 is even still a command we should follow. I believe that it does not, so I do not believe we should be killing witches.

In fact, in Matthew 7:1 (NIV) Jesus says, “Do not judge, or you too will be judged." I know that if I were judged fairly, I would also be condemned to Hell as witches will be.

In fact, we are told to love everyone.

Matthew 22:36-40 NIV
36 “Teacher, which is the greatest commandment in the Law?”

37 Jesus replied: “‘Love the Lord your God with all your heart and with all your soul and with all your mind.’[a] 38 This is the first and greatest commandment. 39 And the second is like it: ‘Love your neighbor as yourself.’[b] 40 All the Law and the Prophets hang on these two commandments.”

It's important to note the context of the command in Exodus 22:18 to not permit a witch to live. It was part of God's covenant with the nation of Israel. There were specific laws given by God to Israel as part of His covenant with them. This covenant began with Abraham, but these laws date from the time of Moses.

Ezekiel speaks of a new covenant that was to come (and has come now in Jesus). So, the old covenant with Israel was in effect from around 1500 B.C. to about 30 A.D.

So, this never applied to Gentiles or any Gentile nation, and it hasn't been in effect for the past 2,000 years anyway.

So, no, we don't have to worry about keeping a covenant that was with the nation of Israel and hasn't been in effect for 2,000 years.

1. I seriously doubt that the "witch" you saw would qualify as the same type of "witch" referred to by that passage.

   The groups that call themselves "witches" today in America* were derived from a neopagan movement started by Gardener and Alexander in the mid 20th century. Despite what some of them claim, none of their paths even existed when the Bible was written (note the "neo" as in "new" -- pagan traditions that pre-dated the Bible or were contemporary with it did not describe themselves as witchcraft, though outsiders sometimes did). I don't know what the Bible was referring to, but it wasn't modern "witchcraft".

   * with the exception of Louisiana Hoodoo, Hatian Vodou, and American Vodun, which were derived from a combination of Roman Catholicism, Native American practices, and West African Vodun -- of these, only Native American traditions might pre-date the old-testament, and they were half a world away from Israel, never described themselves as "witches", and were unlikely to have been a matter of concern in writing the Bible.

2. The command was given specifically to the nation of Israel rather than to all believers, that such things should be against the law within their borders. Since Believers are now spread among the nations, rather than a nation set apart, such a law no longer makes sense.

During the medieval European persecution of witches, there were a lot of arguments about this topic: what is a witch, and what should the church or state do about them? Of course, there were plenty of writers that found Biblical justification from Exodus 22:18, and other passages. There was also an opposing side. One of the most important works from that time is the Discoverie of Witchcraft by Reginald Scot (1584), which comes out very strongly against witch trials.

His main argument is that witchcraft does not exist, but he also says that even if witches could do all the things that witchfinders claimed, that does not mean that they deserve death. He goes at some length through the claimed abilities and practices of witches; it's difficult to summarize, but some of the examples are:

• Controlling the weather: Scot says that only God can do this, citing a great many passages from Scripture (such as Psalm 148:8, "lightning and hail, snow and clouds, stormy winds that do his bidding", and Job 37:12, "[the clouds] are turned around by [God's] counsels, that they may do whatever he commands").

• Killing people: He says that if they do, then they can answer to the civil authority, just like anybody else who kills somebody.

• Curing disease: Again, only God can do this; Scot cites John 10:21, "Can a demon open the eyes of the blind?". He also says that if witches cure with herbs or other plants, they are only using the natural resources that God has given humanity, and should not be condemned.

• Renouncing Christ: Scot believes that they would be wrong to do so, but that impiety does not mean they should be executed. He also mentions that "Peter the apostle renounced, curssed, and forsware his maister and Peters apostacie our Saviour Jesus Christ" (for which see Matthew 26:71-75, Mark 14:69-72, Luke 22:58-62, John 18:15-18). In general, someone who sins should be allowed to repent.

Scot also opposes torture, saying "I doubt not but that the pope ... with lesse compulsion would have renounced the trinitie, and have worshipped the divell upon his knees." This is part of his argument that Biblically-derived principles of justice demand that suspected witches should have a fair trial. This would argue against the kind of harassment that you saw, motivated by simple superstition and ignorance.

The commands God gave to Ancient Israel are normally divided into three kinds: moral, civil and ceremonial. This question and this question have more information. This one, and any of the others invoking the death penalty, certainly fall into the 'civil' category. The state of Israel (loosely speaking) would have the authority to impose the death penalty for a variety of offences, as many states do now.

Christians are no longer expected to obey "the law", which includes this kind of law, though most would say that they are expected to follow the 'moral laws', of which this is not one. That's not to say that 'witchcraft' is now OK,and God approves of it, but the authority to punish with a specific penalty doesn't apply to Christians in these times.

Because 'the state' is given power to punish an offence that does not give a random mob of people the right to harass someone.