One person judges one day to be more important than another day. Someone else judges every day to be the same. Let each one be fully convinced in his own mind.
However, not everyone has this knowledge. Some have been so used to idolatry up until now that when they eat food sacrificed to an idol, their conscience, being weak, is defiled.
I know and am persuaded in the Lord Jesus that nothing is unclean in itself. Still, to someone who considers a thing to be unclean, to that one it is unclean.