«Ideology» means here a collective project, immanent to society, «religion», a collective committment towards an absolute, a transcendent source of meaning and value. To day the ideological belief that we could, by destroying present social structures and the use of new technics, enjory happiness, brotherhood and justice at once becomes a substitute for the absolute of religion.Absolutized ideologies destroy the conditions of meaning in life by dissimulating «the perfect imperfection» of human condition. Ideological eschatology expects «an end of history» located in future time, to be reached under the scientific guidance of political ingenieurs. For religious eschatology, the end of history is transcendent, «beyond time», in eternity. Christians and marxists in search for understanding and common action are usually confusing the future with eternity, immanence with transcendence.Even in a fight to death, transcendence allows a beyond, a dimension of possible brotherhood or communion. After its destruction by absolutisation of an immanent project, there only remains total war and technical power.