There is in Christianity an emphasis on faith that is, to my knowledge, unequalled in any major religion. In most religions, faith is presupposed. In Christianity it is demanded. In general, religions can be summed up with a set of propositions its followers believe, but Christianity is summed up in a person in whom his followers trust. As such, a Christian cannot be characterized solely by fixed beliefs about God, but by a dynamic belief in God.
The need for faith does not end when a person decides to become a Christian; that is, when he or she decides to trust and follow Jesus. Faith is not a passport that gets you into the heavenly country, and then is no longer required. It is more like the currency that is used in that country. Everything a person does in the kingdom of God requires faith.
The Christ-follower moves through life by faith. Four times in Scripture we are explicitly told that the righteous (those people accepted by God) live by faith. No one, no matter how long a Christian or how advanced in spiritual formation, outgrows the need for faith. The Christian life, as St. Paul put it, "is from faith to faith" (Romans 1:17, literal translation).
There is a fascinating example of the importance of faith in the Gospel of John. Before raising Lazarus, Jesus had to tell his disciples the sad news that their friend had died. Many of us have borne that difficult duty, but I doubt any of us ever did it the way Jesus did. He said, "Lazarus is dead and I am glad..." Imagine the shock waves that rolled over the disciples as they heard that their friend was dead and that their master was glad. But Jesus continued: "Lazarus is dead, and I am glad for your sakes that I was not there, so that you may believe."
How important belief must be if Jesus was glad that Lazarus's death afforded his disciples an additional opportunity to believe! And consider who those disciples were: not novices, but apostles. They had been with Jesus night and day, were among the first to believe in him and to declare him Messiah. They had seen him calm a storm, feed thousands with a boy's lunch, and give a congenitally blind man back his sight. And yet Jesus rejoices that these men, who had been with him and believed in him longer than anyone else, were going to have yet another opportunity to believe.
After all the remarkable things the apostles had seen, why would Jesus be excited about a new opportunity for them to believe? He wouldn't be, if faith were nothing more than an arbitrary requirement for entrance into heaven. These men had already believed and had a place reserved for them in heaven. Yet Jesus rejoiced over the prospect of them believing again. What is it about belief that makes it so valuable?
Clearly belief, whatever else it is, is not an arbitrary requirement placed on humans by a self-obsessed God. Faith supplies something that nothing else - reciting a creed or praying five times a day or hopping on one foot - can provide. The very act of believing God does something in a person that nothing else can do.
The reason for that lies in the nature of belief. Trusting God cannot be an unaided act performed to meet a religious obligation, because trust always involves at least two people. It is a collaborative act. In the act of belief, trust meets trustworthiness, faith meets faithfulness. Trust opens the door of one's life to another and, when that other is God himself, transforms those who have it.
Religious rituals alone, no matter how commendable, are incapable of that. Each time a person trusts God, he or she is transformed a little more into the person he or she was meant to be. That's why, when people asked what was required to do God's work, "Jesus told them, 'This is the only work God wants from you: Believe in the one he has sent.'" It is the foundation of everything else.