Being the Abbot of Westminster/London in the 12th century CE Gilbert Crispin (1046-1117) held frequent contacts both personal and official (business) with the local Jewish inhabitants. In his religious dialogue, Disputatio iudaei et christiani, he reflects his conversation with a Jew considering Jewish objections to Christian faith. In contrast to the widespread apologetic attitude towards Judaism, Crispin tries to encounter his dialoguing partner in a friendly way. Both agree on ratio and Scripture as fundamental basis. The present paper argues that Crispin relies on Christological doctrines of the first centuries integrating these traditions into an interfaith dialogue. After presenting an overview of the general argumentation, the logic statements about the two natures (divine-human) of Jesus Christ are examined. This is done by partly quoting the "Jewish" objections to that concept. In addition the Christian responses are discussed. The major aim of this approach is to demonstrate the influence of patristic Christology towards an inter-religious dialogue in the Middle Ages.