This essay was part of an interdisciplinary conference concerning the meaning of relation and consequently of the category “in-between”. This can be illustrated with the Theses for a Trinitarian Ontology written by Klaus Hemmerle. The essay begins with a clarification of the term ‘ontology’. It proceeds with a description of the way Hemmerle develops his ontology on the basis of the spirituality of the Focolare Movement. In this way the death of Jesus, understood as the revelation of the trinitarian God, becomes the key of a relational ontology. Finally the capacity of this kind of ontology for understanding reality is illustrated by the interpretation of the analogical manner of speaking and of social relations.