Nobody else agreed to bring the mother of the witches to Earth; Orisha Nlá made them swear on the Ground not to destroy human lives without cause: that is why the witches have no power against the true children of God or the devoted of Orunmila.
The only force that can beat the force of witchcraft is the ground, the earth. God proclaimed that the ground was to be the only force that would destroy any force or divinity that broke any of the Natural Laws. This decree was proclaimed when a powerful witch of Heaven, called Eye To Yu Oke To Ku Orun, was set on destroying the earthly divinities as a consequence of her wicked conduct on Earth. It was Oshé Sá (Osemolura) who carried the mother of the witches into the world, because nobody else agreed to do it; and the oath Orisha Nlá had the witches take was the Ground.
The oath was taken against the destruction of human lives without cause. This tells us why the witches have no power to destroy the true children of God, or the devoted followers of Orunmila.
The power held by the Elders of the Night (the witches) was given to them by God Almighty, in the time when God lived freely and in body with the divinities. To the witches was given the sole power of keeping watch whenever God took his bath, exactly before the rooster's crow, since it was always forbidden to see God naked. To the witch divinity alone was that power given, and sometimes it was she who gave the rooster the sign that God had taken his bath.
Notes: Oshé Sá tells how God protects us against the powers of witchcraft. The witches destroy whoever deserves it, because men, when men and witches went about as equals, allowed the witch's child to be eaten, and from then on they ruled to finish off the children of the earth.