I am sorry but there is obliviously the translation from Arabic to English has a different meaning to you. for starters Wicca does not believe in god/Allah as being mother nature, it believes in both the God and the Goddess in their many forms and it will depend on the path you take as to what name you call them by it has no relation to any of the three main religions other than it predates all of them and for the better part Christianity uses the Sabbaths of wicca as there own, there is, I agree white and dark but this becomes a grey area as to where the line is drawn and you cross over from one to the other, this will also depend whether you are a solitary practitioner or you belong to a coven. Necromancy is again not just conversing with spirits it is summoning as I stated there are those who claim to practice necromancy that also claim they use this summoning to bring the dead back to life and has in the past been likened to Voodoo for this part. Wicca and Necromancy are too different paths wicca does not encourage the summoning of the dead to do ones bidding infact it does not use any form of summoning of the dead at all, wicca invokes the gods and their many forms and this is how the "spell" is cast.
I don't need someone who obliviously still knows little about what he delves into to teach me the difference. It is a subject that I am very experienced in and believe me when I say my information does not come from a television set.