The paper aims to address the crisis of thinking on disused churches. The trans-disciplinary research on the history of the theoretical research on disused churches from Vatican II (1962-1965) until the Vatican guidelines on disused churches (2018) is proposed to review that to understand the reasons of this crisis. First of all, the distinction between the theoretical research on the sacred space of disused churches and on the building of disused churches, which has emerged in all important ecclesiastical, national (Germany, Province of Quebec, Belgium, France, the Netherlands and Italy) and international scientific papers, will be presented. Secondly, the reasons of the presence and of the absence of the sacred space in the thinking on disused churches will be valued with the writings of the philosopher of religion Romano Guardini (1885-1968) on the sacred space and art. Finally, Guardini's scientific method of the 'two contrapositions' ('Gegensätze') for the 'contemplative knowledge' (Anschauung) of the world will be explained as an instrument to understand when the thinking on the past and on the future of the sacred space of disused churches is contradictory and when is in the polar tension through few case studies of European disused churches converted to diocesan museums.