John Chrysostom
"Do not destroy the work of God for the sake of food." By the work of God he means the salvation of the brother, and he intensifies fear by showing that the man who scandalizes his brother acts against what God cares for. You not only fail to build up, as you think, says the Apostle, but you destroy. Moreover, you destroy not a human work, but God's work, and not for anything important, but for a trivial thing, "for the sake of food." Then, lest by such condescension he confirm the brother in an evil disposition. He again states the general principle, saying, "All things indeed are pure, but it is evil for the man who eats with stumbling," that is, with an evil conscience. Thus, if you compel him and he eats, there will be no benefit in it.
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Foods do not make a man unclean; the disposition with which you eat does. Therefore, if you do not correct the disposition, all your labor is vain and even harmful. For it is not the same thing to consider something unclean and, considering it unclean, to eat it. In the latter case you sin doubly, strengthening the prejudice by your obstinacy and compelling him to eat what is unclean. Therefore, until you have persuaded him, do not compel him.