The mercy as a category of social life automatically enters into the social relations subject to legal regulation. In addition to the objective dimension, it is associated with a certain attitude, which is based on the affirmation of a man, showing him compassion and opening the way to repair the broken relations. Today, it is necessary to bolderly determine the axiological foundations on which the system of rights is built in the Christian cultural context. This mainly applies to the Constitution. On this basis, it would be possible to discover elements that content and functionally complement the principle of justice in law, which correspond to the principle of mercy. Although mercy does not belong to the dictionary of legal concepts, its establishment in it seems possible and desirable. The content-rich concept of mercy is progressively rooted in the social consciousness. The introduction of it into the legal system may be greater flexibility of the law, its more specific and individual character and greater closeness to life.