Howbeit there is not in every man that knowledge: for some with conscience of the idol unto this hour eat it as a thing offered unto an idol; and their conscience being weak is defiled. There is not in every man that knowledge - This is spoken in reference to what is said, 1 Corinthians 8:4 : We know that an idol is nothing in the world; for some with a conscience of the idol, viz. that it is something, eat it - the flesh that was offered to the idol, as a thing thus offered, considering the feast as a sacred banquet, by which they have fellowship with the idol. And their conscience being weak - not properly instructed in Divine things, is defiled - he performs what he does as an act of religious worship, and thus his conscience contracts guilt through this idolatry.
As in the commencement of Christianity, among the Jews that were converted, there were many found who incorporated the rites of the law with the principles of the Gospel; so, doubtless, among the Gentiles, there were several who did not at once throw aside all their idolatry or idolatrous notions, but preserved some of its more spiritual and imposing parts, and might think it necessary to mingle idolatrous feasts with the rites of Christianity; as the sacrament of the Lord's supper was certainly considered as a feast upon a sacrifice, as I have proved in my Discourse on the Nature and Design of the Eucharist. As the minds of many of these young Gentile converts could not, as yet, have been deeply endued with spiritual knowledge, they might incorporate these feasts, and confound their nature and properties.