Sorry but the ignorance is not mine:

“ Thou shalt not suffer a witch to live. — The word translated “witch” in this passage is the feminine singular of that rendered by “sorcerers” in Exodus 7:11, and means “a mutterer of charms.” The use of the feminine form can only be accounted for by supposing that, practically, witchcraft was at the time mainly professed by females. Whether “witches” had actual help from evil spirits, or only professed to work magical effects by their aid, the sin against God was the same. Jehovah was renounced, and a power other than His invoked and upheld. Witchcraft was as much rebellion against God as idolatry or blasphemy, and deserved the same punishment.” http://biblehub.com/commentaries/exodus/22-18.htm

This is Old Testament, Jewish Torah wording. Whether the aramaic word is translated as Witch, or as Sorceress, the meaning is the same. It does not mean “poisoner” although many witches’ curses were probably effected through poisoning their victims. There may be Witches who think they are Christian but they cannot be Christian unless they renounce Witchcraft first. The logic is clear: so-called Christian Witches are deluding themselves, lying to you or both.