Who therefore can deny that it is a wicked superstition that men kneel down before bread, to adore Jesus Christ in it? There is no doubt that the Council of Nicaea wanted to prevent such an detriment, having prohibited Christians from stopping to fix their thoughts humbly toward visible signs. There would not have been any other reason why it was instituted in the ancient Church that the deacon would cry out to the people in a loud and clear voice before the consecration [of the elements], that everyone should have his heart up above. And in the same way the Scripture, other than explaining to us distinctly the ascension of our Lord, when it mentions Him, exhorts us to raise our hearts up above (Col. 3:1) to remove from us from any carnal thought. Therefore, following this rule, it is necessary for us to adore Him spiritually in the glory of heaven, rather than to invent such a dangerous form of adoration, which proceeds from a deep dream and worse than carnal, that we conceive as being from God and from Jesus Christ.
That is why those who invented the adoration of the sacrament, did not only think it up by themselves without Scripture, in which not a single word is found of it, that which would not have been forgotten, if it had been approved by God, but they also forge a new god plainly contrary to the Scriptures, according to their own will, and forsake the living God. For what idolatry is there in the world, if that is not one, to adore the gifts instead of the Giver? In this they have doubly erred: for the honor was taken from God, to transfer it to the creature. And God was also dishonored, in that the gift of His goodness was soiled and profaned, when an execrable idol was made of His holy sacrament.
We, however, in order that we do not fall into the same ditch, let us fix our ears, our eyes, our hearts, our thoughts, and our tongues, entirely in the very holy teaching of God. For it is in the school of the Holy Spirit, a very good Teacher, in which there is excellent benefit, to which there is no need to add anything else, and it is to voluntarily ignore everything that is not taught in it.
Jean Calvin, Institution Chrétienne, IV.XVII.36