We can show them why what they practice is in fact idolatrous without misrepresenting their views. It is not misrepresenting their views to say that what they are do is idolatry and giving worship to creatures, but it would be misrepresenting their views to say they consider what they do to be worship.
John Calvin wrote, “But it is necessary to attend to the observation with which I set out—viz. that unless everything peculiar to divinity is confined to God alone, he is robbed of his honour and his worship is violated. It may be proper here more particularly to attend to the subtleties which superstition employs. In revolting to strange gods, it avoids the appearance of abandoning the Supreme God, or reducing him to the same rank with others. It gives him the highest place, but at the same time surrounds him with a tribe of minor deities, among whom it portions out his peculiar offices. In this way, though in a dissembling and crafty manner, the glory of the Godhead is dissected, and not allowed to remain entire. In the same way the people of old, both Jews and Gentiles, placed an immense crowd in subordination to the father and ruler of the gods, and gave them, according to their rank, to share with the supreme God in the government of heaven and earth. In the same way, too, for some ages past, departed saints have been exalted to partnership with God, to be worshipped, invoked, and lauded in his stead. And yet we do not even think that the majesty of God is obscured by this abomination, whereas it is in a great measure suppressed and extinguished—all that we retain being a frigid opinion of his supreme power. At the same time, being deluded by these entanglements, we go astray after divers gods. 2. The distinction of what is called δυλια and λατρια was invented for the very purpose of permitting divine honours to be paid to angels and dead men with apparent impunity. For it is plain that the worship which Papists pay to saints differs in no respect from the worship of God: for this worship is paid without distinction; only when they are pressed they have recourse to the evasion, that what belongs to God is kept unimpaired, because they leave him λατρια. But since the question relates not to the word, but the thing, how can they be allowed to sport at will with a matter of the highest moment? But not to insist on this, the utmost they will obtain by their distinction is, that they give worship to God, and service to the others. For λατρεὶα in Greek has the same meaning as worship in Latin; whereas δουλεὶα properly
means service, though the words are sometimes used in Scripture indiscriminately. But granting that the distinction is invariably preserved, the thing to be inquired into is the meaning of each. Δουλεὶα unquestionably means service, and λατρεὶα worship. But no man doubts that to serve is something higher than to worship. For it were often a hard thing to serve him whom you would not refuse to reverence. It is, therefore, an unjust division to assign the greater to the saints and leave the less to God. But several of the ancient fathers observed this distinction. What if they did, when all men see that it is not only improper, but utterly frivolous?
3. Laying aside subtleties, let us examine the thing. When Paul reminds the Galatians of what they were before they came to the knowledge of Gods he says that they “did service unto them which by nature are no gods,” (Gal. 4:8). Because he does not say λατρια, was their superstition excusable? This superstition, to which he gives the name of δυλια, he condemns as much as if he had given it the name of λατρια. When Christ repels Satan’s insulting proposal with the words, “It is written, Thou shalt worship the Lord thy God, and him only shalt thou serve,” (Mt. 4:10), there was no question of λατρια. For all that Satan asked was προσκὺνεσις (obeisance). In like manners when John is rebuked by the angel for falling on his knees before him (Rev. 19:10; 22:8, 9), we ought not to suppose that John had so far forgotten himself as to have intended to transfer the honour due to God alone to an angel. But because it was impossible that a worship connected with religion should not savour somewhat of divine worship, he could not προσκὺνει̑ν (do obeisance to) the angel without derogating from the glory of God. True, we often read that men were worshipped; but that was, if I may so speak, civil honour. The case is different with religious honour, which, the moment it is conjoined with worship, carries profanation of the divine honour along with it. The same thing may be seen in the case of Cornelius (Acts 10:25). He had not made so little progress in piety as not to confine supreme worship to God alone. Therefore, when he prostrates himself before Peter, he certainly does it not with the intention of adoring him instead of God. Yet Peter sternly forbids him. And why, but just because men never distinguish so accurately between the worship of God and the creatures as not to transfer promiscuously to the creature that which belongs only to God. Therefore, if we would have one God, let us remember that we can never appropriate the minutest portion of his glory without retaining what is his due. Accordingly, when Zechariah discourses concerning the repairing of the Church, he distinctly says not only that there would be one God, but also that he would have only one name—the reason being, that he might have nothing in common with idols...He has been pleased to prescribe in his Law what is lawful and right, and thus restrict men to a certain rule, lest any should allow themselves to devise a worship of their own. But as it is inexpedient to burden the reader by mixing up a variety of topics, I do not now dwell on this one. Let it suffice to remember, that whatever offices of piety are bestowed anywhere else than on God alone, are of the nature of sacrilege. First, superstition attached divine honours to the sun and stars, or to idols: afterwards ambition followed—ambition which, decking man in the spoils of God, dared to profane all that was sacred. And though the principle of worshipping a supreme Deity continued to be held, still the practice was to sacrifice promiscuously to genii and minor gods, or departed heroes: so prone is the descent to this vice of communicating to a crowd that which God strictly claims as his own peculiar right!” (Institutes of the Christian Religion, Book I, Chapter 12)