Eucharist a key doctrine

I've been enjoying reading about John Williamson Nevin (1803-1886) and the Mercersburg Theology in Mathison Given For You.

Mathison says (p139):

As Gerrish explains, the defense of the correct doctrine of the Eucharist was crucial to Nevin because in his judgement “what a man thinks of the Holy Eucharist is a plain index to what he will think of Christ, the church, and theology itself. Citing B. A. Gerrish, Tradition and the Modern World: Reformed Theology in the Nineteenth Century (Chicago, University of Chicago Press, 1978), 58-59.

And here are some bits of Nevin:

…

the Eucharist forms the very heart of the whole of Christian worship… Mystical Presence, p3

Our view of the Lord’s Supper must ever condition and rule in the end our view of Christ’s person and the conception we form of the Church. It must influence at the same time, very materially, our whole system of theology, as well as all our ideas of ecclesiastical history. p3

The eucharistic doctrine of the sixteenth century was interwoven with the whole church system of the time; to give it up, then, must involve in the end a renunciation in principle, if not in profession, of this system itself in its radical, distinctive constitution. p3

The Question of the Eucharist is one of the most important belonging to the history of religion. It may be regarded indeed as in some sense central to the whole Christian system. For Christianity is grounded in the living union of the believer with the person of Christ; and this great fact is emphatically concentrated in the mystery of the Lord’s Supper; which has always been clothed on this very account, to the consciousness of the Church, with a character of sanctity and solemnity, surpassing that of any other Christian institution. Mystical Presence p51 (Mathison, p139-140)

The doctrine of the eucharist is intimately connected with all that is most deep and central in the Christian system as a whole; and it is not possible for it to undergo any material modification in any direction, without a corresponding modification at the same time of the theory and life religion at other points. If it be true then, that such a falling away from the eucharistic view of the sixteenth century, as is now asserted, has taken place in the Reformed Church, it is very certain that the revolution is not confined to this point. It must affect necessarily the whole view, that is entertained of Christ’s person, the idea of the Church, and the doctrine of salvation throughout. Not that the change in the theory of the Lord’s Supper may be considered the origin and cause, properly speaking, of any such general theological revolution; but because it could not occur, except as accompanied by this general revolution, of which it may be taken as the most significant exponent and measure. Mystical Presence p52 (Mathison, p140-141)