Jesus said that they were not entering into the Kingdom of Heaven and were preventing others from entering. They were nothing but stumbling blocks. Jesus called them hypocrites. He said they were like sepulchres that look good on the outside, but are full of uncleanness inside. On the outside they appeared to be righteous, but on the inside they were full of hypocrisy and sin.
There are people today who feel that as long as they go to church on Sunday, they can live as they like during the rest of the week. This is not right. People like that are only stumbling blocks to those who are really trying to serve God. Unless we have asked Jesus to forgive us of our sins and be the Lord of our life, we have nothing.
It's not important how we look on the outside. What counts is what we are on the inside. Jesus said that if anyone offended the ones who believe in Him, it would be better if a millstone was hanged around his neck and he was cast into the sea. Be very careful that your walk matches your talk. Don't be all show, with nothing inside.