Every religion except for true, biblical Christianity does not deal with the heart. Roman Catholicism and Eastern Orthodoxy are not included as part of Christianity, because they are cultic, and a perversion of God's Word. In fact, as the Spirit of God was operating on Martin Luther's heart, he would confess his sins to the priest. One time, he confessed that he coveted brother so-and-so's soup. The priest told him to confess something worthwhile and interesting!
Another example of this is the mantra that the Eastern Orthodox priests say when their confessors come: "Confess to me all you have done."
Jesus Himself was clear that it was the heart that was sinful. Have you ever struggled with your own heart? True, biblical Christianity is hard because we have to deal with and conquer our own sinful hearts. All other religions only deal with the outside. Anyone can pray five times a day toward Mecca and recite formulas. Anyone can confess the "big sins" to a priest and then go away and lust after their co-worker, because, after all, at least they didn't actually commit adultery with them. Anyone can live in this kind of a moralistic fashion.
This is why the gospel is not for everyone. I am not saying that we should not preach the gospel to all; we should. I am saying what our Lord Jesus Himself said: The gospel is for those who are blind, who are poor, who are sick, and who are tired of their own righteousness. The gospel is not for those who think they are basically good. The gospel is for those who know that there is nothing good that dwells in them.
Christ did not come to call the righteous, but sinners to repentance. It is not the healthy who needs a doctor, but the sick. Since the Pharisees claimed they could see, their guilt remained.
O Lord, show us by Your grace that we are blind, sick, poor, and wretched. Justify us solely by the perfect righteousness of the Lord Jesus Christ. Sanctify us by cleaning our putrid hearts and writing Your most Holy Law upon them, and preserve and bring us to the very end. In the precious Name of our perfect Savior, the Lion of Judah. Amen.