One of the saddest mistakes of the modern age is that we seem to have reduced Christianity to believing in Jesus and being nice. We behave as if all we have to do is be a nice person and when we die we go straight to heaven.
If it were simply about being a nice person we could be Buddhists or follow pretty much any philosophy or religion. Despite the western misconception, even Islam teaches its followers to be nice, to help the poor, etc.
God did not become incarnate, suffer and die on a cross, just to give us another set of ethical rules, or to repeat the Ten Commandments. To be a Christian is to have a completely new relationship with God and a new relationship with one another.
Jesus redefined what it means to be human.
For his part Jesus makes it possible for us to actually share the divine life. In exchange Jesus raises the demands on us.
I tell you, unless your righteousness surpasses that of the scribes and Pharisees, you will not enter the kingdom of heaven.
It is not enough for us not to murder. We must love our enemies.
It is not enough for us not to steal. We must limit our consumption and give to the needy.
It is not enough for us not to commit adultery. We must not do anything that misuses our sexuality or objectifies another human being.
And it is possible for us to do all of this precisely because we do it not as lone persons but as members of the Church, and have access to God's grace. Through our regular reception of the sacraments we can constantly renew the grace of God, and that grace can empower us to overcome even the most engrained of our behaviors.
Being a nice person does not make you a Christian. Simply acknowledging Jesus Christ as your Lord and Savior does not make you a Christian. To be a Christian means to live as a member of that family we call the Church, to receive the gift of God grace in the sacraments, and so be able to live a "righteousness that surpasses that of the scribes and Pharisees."