St John Cassian’s treatise on the Incarnation is of a very different character to his better-known works of spirituality, the Institutes and the Collations. Written in 429, it was part of the build-up to the condemnation of Nestorius in 430 and 431. The doctrine of the nature of Christ remained largely intact, even through the upheavals which afflicted Christendom during the sixteenth century, so that Catholics, Orthodox and Protestants could at least agree on that.

That all changed in the twentieth century, when the ‘modernist’ or ‘liberal’ movement in theology gained control over most Protestant and many Catholic writers. Many moderns, who still claim to be Christians, have consciously of unconsciously revived all the erroneous opinions which Cassian nicely terms the ‘weeds’ in the garden of God.

Cassian teaches the fundamental Catholic principle of ongoing revelation through both Scripture and Tradition, and the authority of the living Church. In support of his work, he quotes the Fathers, the great writers who have been accepted as authoritative by Orthodox and Catholic alike, although of course they were his own actual or near contemporaries. He shows how the true interpretation of the Bible leads only to a Catholic conclusion: Jesus Christ is true God and true Man.