G.K. Chesterton once said that the best argument against Christianity is Christians. That is certainly true of Catholicism. Pope John Paul II, putting it politely, says,
"The Catholic Church does not forget that many among her members cause God's plan to be discernible only with difficulty." (
Ut Unum Sint, 11).
But is that really an argument against the truth of the faith? I don't see how. To argue that Catholicism is untrue because it doesn't transform the lives of those who don't practice it, is like arguing that aspirin doesn't work because it doesn't relieve the headaches of those who don't take it.
The Church only claims to announce the Good News of Jesus Christ, and it invites everyone to embrace the life of grace He offers. It does not claim that people who spurn its teachings and reject its life will be transformed into faithful disciples anyway. Nor does it claim that being born to Catholic parents guarantees that a person will inherit his parents' faith.
If you want to see the fruit of the Catholic faith, you have to look at the people who are committed to the faith, who take it seriously and put it into practice every day.
It's pointless to look at those who are cultural Catholics only, who say they're Catholic if you ask them, but who don't try to live the life, even though they may go to Mass out of habit, or guilt, or whatever. People aren't magically transformed into good Christians just by walking into a Catholic church (even if they do it every week).
Repentance and conversion of heart are the keys to the Christian life. Without them, everything else is sterile and false, whether one calls oneself "Catholic" or not.
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How Can Catholicism Be True When Catholics Are So Dead?