It is "prepared from eternity to eternity."
What went on before, back in the first "eternity?" We read elsewhere of this peaceful existence during "millennial" conditions, which end with rebellion, disputes and a war. Was Satan loosed in an earlier eternity after some season of peace to stir the hearts of men to anger one with another? (See Rev. 20: 7-9.) Was he cast out to hell, or the Telestial Kingdom, where we presently reside? What went on? How often would the Lord have gathered us as a hen gathers her chicks, but we would not be gathered? (I suppose His asking and the lack of an answer implies a great number.)