1 Corinthians 10:27

If one of them that believe not biddeth you to a feast, and ye are disposed to go; whatsoever is set before you, eat, asking no question for conscience' sake. But if any man say unto you, This hath been offered in sacrifice, eat not, for his sake that showed it, and for conscience' sake.

This was Paul's answer to the third question, which regarded eating as a guest in the home of an unbeliever. Paul's command was full of reason and consideration. The Christian was not to raise any question whatever about the meat served; but, on the other hand, if the meat was definitely identified by "any man" as having been offered to idols, then the Christian should not indulge in it. Thus, by his firm and unequivocal answer to the three solemn questions propounded by the Corinthians, Paul enforced the absolute abstinence on the part of Christians from anything that was identified as a sacrifice to an idol. Where does that leave the "all things are lawful" proposition?

Before leaving this, the words of Farrar should be noted:

How gross was the calumny which asserted that Paul taught men to be INDIFFERENT about eating things sacrificed to idols! He taught indifference only in cases where idolatry could not be directly involved in the question. He only repudiated the idle superstition that the food became INHERENTLY tainted by such a consecration when the eater was unaware of it.[33]