Sadly, "...illumination...by his Word and Spirit" can be stymied by ill-will, intransigence, self-interest (and in the case of women misogyny) of authority and the perversity or disinterest of non-authority. One can only have faith in the ultimate "illumination" on so many levels. If one believes that post-Resurrection God works through Christ-ian humanity what will "tip the balance" - "legitimate teaching authority" or "the faithful" (member and dis-membered)?
Pope Francis and the disintegrating church are softening up one end of the fulcrum. Until "we" man with women stand for total peership in equivalent torque I doubt anything will happen.
That will be the Spirit illuminating.