Cusa is part of an irenical tradition that goes from Abelard to Roger Bacon to Raimondo Lullo to Pico della Mirandola or, in particular, to Thomas More.
Cusa does not want to sacrifice the truth on the altar of politics, like all temporal powers do, the main causes of a bad diversity, just like a bad unity, in religious matters. They adapt their spiritual life to utilitarist and pragmatic hypotheses, the validity of which still has to be demonstrated. Cusa does not even agree with moralising irenism, which tends to make do with good sentiments and whose efficacy is more or less of no value, due to the non-consideration of the real depth of the problem of evil.
The literary form is that of a dialogue in heaven. Cusa dreams of uniting the religions in a universal congress in Jerusalem, the rough outline of which is to be discussed in Heaven in a conclave presided over by the Word of God, and which Cusa came to know about in a dream.
Three directions, in his method to unite religions. A first one, more theological, tends to confirm that all religions implicitly say the same thing about Christianity, if correctly expressed. A second one, more mystical-philosophical, the contents of which would be transcendent to all dogmatics because everything is reabsorbed into the ineffable unity, which is the last word of Cusa’s metaphysics; but this religion would be the authentic Christianity. A third one uses polyritism as a model to think of religious unity. ‘It will be the end of hate […] and everyone will know that only one religion exists in the diversity of rites’. Behind this accomplishment is to be found Master Eckhart’s system. ‘Nicola’s thought is above all metaphysical. It is founded on his oenology’ (pp. 46-47).
The method of debate consists in explaining the dogmas in an orthodox way, thinks Cusa, and in such a way that the non-Christian of good faith cannot help but recognise himself in the Christian doctrine. Reciprocally, he considers that, with a deeper approach, the other religions would come closer to Christ who has said he is the Truth. This presupposes a certain Agnosticism, so that it is as if the whole world is led back to the same point, that of an ‘approximation that will never reach its end: the divine One is the obscure one’ (p. 54).
On the one hand Cusa perhaps excessively reduces the other religious forms to the unity of Christian faith, on the other hand he impoverishes the latter, debasing rites, sacraments and institutions. In the De pace fidei, the Church is not mentioned. Cusa puts the essential into pure spiritual which would consist above all of a mystical entrance into nothingness and the obscure, in a sort of reintegration of the One. Thus it can be assumed that everyone is in agreement over the essential. But the danger is that Cusa and his disciples find themselves alone, agreeing among themselves but separate from other believers, among whom few would recognise the reality of their religious life in the refinement of these unbridled dialectics.
The logic of the reintegration of the One is considered valid in order to establish the articles of Christian dogmatic thought as necessary.
This dogmatics, as far as being understood as a religious philosophy, would be implicitly found in all religions. For Cusa perhaps, Jesus Christ in flesh and blood exists historically, but one however has the impression that He tends to be only a necessary moment of a system in which history is taken away from the concept like a rabbit from a top-hat. As Christ is the absolute Truth, and the subject of all philosophers, the Christians have the explicit faith in historical Christ as their own, while the others possess this faith in an implicit way, so that it is sufficient to make themselves explicit in order to reach the Christian faith.