John Calvin writes,

“Moreover, two faults are here to be avoided. We must neither, by setting too little value on the signs, dissever them from their meanings to which they are in some degree annexed, nor by immoderately extolling them, seem somewhat to obscure the mysteries themselves. That Christ is the bread of life by which believers are nourished unto eternal life, no man is so utterly devoid of religion as not to acknowledge. But all are not agreed as to the mode of partaking of him. For there are some who define the eating of the flesh of Christ, and the drinking of his blood, to be, in one word, nothing more than believing in Christ himself. But Christ seems to me to have intended to teach something more express and more sublime in that noble discourse, in which he recommends the eating of his flesh—viz. that we are quickened by the true partaking of him, which he designated by the terms eating and drinking, lest any one should suppose that the life which we obtain from him is obtained by simple knowledge.” – Institutes of the Christian religion, IV, 17