The idea of the Church as a divinely ordained living organism, or 'Body of Christ'

The idea [or metaphor] of the Church as a divinely ordained living organism, or 'Body of Christ', was commonplace in early medieval ecclesiology.

https://en.wikipedia.org/wiki/Body_of_Christ

The importance of the organism in the political theory of John of Salisbury
https://doi.org/10.1017/S0143045900003355  https://goo.gl/ZXAh8Q

also in

Michael Wilks (1994). The World of John of Salisbury. Blackwell. ISBN 978-0-631-19409-5. pp 303-17

THE PHYSIOLOGICAL SIGNIFICANCE OF THE ORGANIC METAPHOR IN JOHN OF SALISBURY'S "POLICRATICUS"

Cary J. Nederman
History of Political Thought
Vol. 8, No. 2 (Summer 1987), pp. 211-223
Published by: Imprint Academic Ltd.
Stable URL: http://www.jstor.org/stable/26213292

John of Salisbury: Policraticus (Cambridge Texts in the History of Political Thought) - Internet Archive

John of Salisbury and Pseudo-Plutarch
Author: H. Liebeschütz
Source: Journal of the Warburg and Courtauld Institutes, Vol. 6 (1943), pp. 33-39
Published by: The Warburg Institute
Stable URL: http://www.jstor.org/stable/750420...
In Books V and VI [of the Policraticus John of Salisbury] leaves the Bible and arranges his material in terms of a new frame of reference: res publica is symbolized by the human body, and it is in terms of this image that John presents his analysis of the social organism. The head of the body politic is the king; the soul is the priest; the senate is the heart; the judges and administrators of the provinces are the eyes, ears and tongue; the knights are the hands and the peasants are the feet. It is the duty of the prince to keep the organism in good health, and in this the priesthood is pledged to help him; the relationship between church and state being expressed in terms of the relationship between soul and body. And it is this metaphor which determines the orders of the chapters in these two books.

There is no new feeling here for the character and organic unity of the state. John is expressing the common mediaeval conception of society as ecclesia, coming under two authorities, the spiritual and the secular, which have to work together in harmony.
...

The head of the body politic, the king or prince, is literally the "Head" of state.