Food Sacrificed for Idols
According to the Gospel of Mark, Jesus supposedly said the following:
Again Jesus called the crowd to him and said, "Listen to me, everyone, and understand this. Nothing outside a man can make him 'unclean' by going into him. Rather, it is what comes out of a man that makes him 'unclean.' "[a] After he had left the crowd and entered the house, his disciples asked him about this parable. "Are you so dull?" he asked. "Don't you see that nothing that enters a man from the outside can make him 'unclean'? For it doesn't go into his heart but into his stomach, and then out of his body." (In saying this, Jesus declared all foods "clean.") He went on: "What comes out of a man is what makes him 'unclean.' (Mark 7:14-20)
So according to Jesus, foods that come into you don't make you unclean, as they only go into your stomach, but not to your heart. It's what comes out of you that makes you unclean, such as things you say, or things you do. The fact that Jesus mentions the heart shows he is talking about something spiritual here, something to do with the faith.
Now indeed, some might read this teaching and think that yes this is a teaching that makes perfect sense, yet the reality is that this teaching is actually wrong. The reason it's wrong is because there are foods that can come into you and make you unclean, not physically unclean, as that wasn't what Jesus was talking about, but SPIRITUALLY UNCLEAN.
Did Jesus forget about the foods that were sacrificed to idols? What if a man ate food that was sacrificed to idols because it was part of his faith, part of his pagan belief, the act of eating that food would make him completely spiritually unclean because he has taken part in a pagan ritual that he believes in, and this act of taking the food in is connected to his heart, because it's part of his spiritual faith!
And Allah Knows Best!