27 If an unbeliever invites you to a meal and you want to go, eat whatever is put before you without raising questions of conscience. 28 But if someone says to you, “This has been offered in sacrifice,” then do not eat it, both for the sake of the one who told you and for the sake of conscience. 29 I am referring to the other person’s conscience, not yours. For why is my freedom being judged by another’s conscience? 30 If I take part in the meal with thankfulness, why am I denounced because of something I thank God for?—1 Cor. 10:27-30 NIV
Jesus set the example of eating with sinners and he expects us to do the same. We are free to eat whatever is served to us. In those days, it was very possible that a person could have been offered something that was prepared as a sacrifice to an idol. If they were informed of that, then they should not partake of that food, not because it is a sin for them, but for the sake of the other person. Why? Paul is using the eating of meat that has been sacrificed to idols to show us an example of how we should be willing to give up certain rights rather than offend or harm another person. We are not judged by what goes into our mouth but by what comes out of it.
10 Jesus called the crowd to him and said, “Listen and understand. 11 What goes into someone’s mouth does not defile them, but what comes out of their mouth, that is what defiles them.”–Matt. 15:10,11 NIV
If we profess one thing and do another, we not only harm the Kingdom of God and ourselves, we also become a stumbling block to unbelievers and weaker brothers and sisters. If we know something offends another person even though it would not be a sin for us to take that action, then we should abstain from doing so in their presence. The only exception would be that if, in so doing, we had to violate our own conscience, then that is a line we cannot cross.