Some of the Lord's followers think one day is more important than another. Others think all days are the same. But each of you should make up your own mind.
The Lord Jesus has made it clear to me that God considers all foods fit to eat. But if you think some foods are unfit to eat, then for you they are not fit.
But if you do have doubts about what you eat, you are going against your beliefs. And you know that is wrong, because anything you do against your beliefs is sin.
Not everyone knows these things. In fact, many people have grown up with the belief that idols have life in them. So when they eat meat offered to idols, they are bothered by a weak conscience.