1 Corinthians 8:7

Howbeit, there is not in every man that knowledge
The apostle is not speaking of Heathens, in whom there was no knowledge of the one true God, the author of all things, and of the one Lord Jesus, the only saviour and Redeemer; but of Christians, in whom there was the knowledge of these things, but not in all of them; the knowledge of this, that an idol was nothing; for though they knew that an idol was not God, and had no true deity in it, nor was it any true representation of God, yet fancied that it had an influence upon food that was offered to it, to defile it, and render it unclean, so that it ought not to be eaten; and since there were such persons that were so ignorant and weak, it became those who had more knowledge to be careful how they laid stumblingblocks in the way of such, to the prejudice of their consciences: that there were such, the apostle affirms,

for some with conscience of the idol unto this hour, eat it as a
thing offered unto an idol;
that is, there were some persons even at that very time, though they had been so long converted from Heathenism to Christianity, yet had such an opinion of an idol, that they really thought in their own consciences, that there were something in an idol, they could not well tell what, that defiled meats offered to it, and made them unlawful to be eaten; and yet, through the influence of the example of others, were prevailed upon to eat of them, having at the same time a notion of such food, as if it was not common food, but had received some virtue from the idol; and not without some regret, and uneasiness of mind, as being polluted with it. The Alexandrian copy, and some others, read, (sunhyeia) "through custom of the idol"; and so the Ethiopic version seems to have read: and the sense is, that some having been formerly accustomed to worship idols, and to eat things offered to them, as having received some virtue from them, still retained an opinion, that there was some difference between such meats and others.

And their conscience being weak is defiled;
because such act against the dictates of their own conscience; which, though weak, is binding, and sinned against, defiles, according to the rules given by the apostle, ( Romans 14:14 Romans 14:23 ) .