The term spiritual as here used, it must always be borne in mind, carries in it no opposition to the idea of substance; nor does it refer to the person of Christ simply as it is spirit, and not body. On the contrary, it has regard to the inmost substance of his body itself. All imagination of a material intermingling of Christ’s flesh with ours is indeed carefully removed; but it is only to assert the more positively a real participation in the true life of his flesh as such. The communion is with the Savior’s body and blood, the very essence of which under a spiritual form, is carried over into the believer’s person. If this be not the meaning of the Westminster Assembly; if in the use of language, borrowed here so plainly from the creed of Calvin and the Reformed Church generally in the sixteenth century, the Assembly intended to signify after all something quite different from that creed, a mere moral union with Christ for instance, a communication with him in his divine nature simply, or an appropriation only of the merits of his life and death; it will be found very hard, in the first place to put any intelligible sense whatever into their words, and more difficult still, in the second place, to vindicate the interpretation as worthy either of their wisdom or their truth.
J.W. Nevin, 1846, The Mystical Presence 112-113