The paper examines the relationship between reason and faith. It aims at the justification of faith not as the rival of reason, but rather as its constitutive element, which not only does not deny it, but is, on the contrary, its original foundation. This claim is seen as resulting from the dismissal of the naive realism through the examination of human subjektivity. In trying to define faith the author examines its role and functions in secular as well as in religious reasons. In justifying the need and the sense of faith he formulates a spiritual law governing the human life, namely the law of assimilation.