4. "I don't need to go to Church. As long as I'm a good person, that's all that really matters."
This argument is used often, and is pretty disingenuous. When someone says he's a "good person," what he really means is that he's "not a bad person"
-- bad people being those who murder, rape, and steal. Most people don't have to extend a lot of effort to avoid these sins, and that's the idea: We want to do the least amount of work necessary just to get us by. Not very Christ-like, is it?
But that mentality aside, there's a much more important reason why Catholics go to Church other than just as an exercise in going the extra mile. Mass is the cornerstone of our faith life because of what lies at its heart: the Eucharist. It's the source of all life for Catholics, who believe that bread and wine become the real body and blood of Christ. It's not just a symbol of God, but God made physically present to us in a way we don't experience through prayer alone.
Jesus said, "Truly, truly, I say to you, unless you eat the flesh of the Son of man and drink his blood, you have no life in you; he who eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day" (John 6:53-54). We're honouring Jesus' command and trusting in that promise every time we go to Mass.
What's more, the Eucharist -- along with all the other Sacraments -- is only available to those in the Church. As members of the Church, Christ's visible body here on earth, our lives are intimately tied up with the lives of others in that Church. Our personal relationship with God is vital, but we also have a responsibility to live as faithful members of Christ's body. Just being a "good person" isn't enough.
Benedict on the Mass