Knowledge vs. Faith
The first of the Ten Commandments is, "I am the Lord your God, Who brought you out of the land of Egypt..." The Sages ask: What exactly is this commanding us to do? Surely, it is a statement, not a commandment.
As a result, some commentaries answer that there are in fact only nine commandments; but who ever said there were 10? The Hebrew is aseret hadibrot - the ten "statements," not "commandments."
Most commentators, however, do consider this first line to be a commandment. They say that it is an obligation to "know" that God exists.
The Malbim, a 19th century commentator asks a famous question on this. It is absolutely impossible that anyone should command you to know that they exist. Follow this reasoning: If you know that they exist already, then there is no need for a command. And if you do not know that they exist, then who is commanding you?! In other words, why should you take seriously the command of someone you don't think exists? And if you think he does exist, then the command to know that he exists becomes superfluous!
The Malbim answers very simply: Many people have faith that God exists. They feel it, but are unsure exactly why. The first of the Ten Commandments is to know that God exists - not to believe, to have faith, or to sort of "think it to be the case." The Torah says you must examine the evidence and come to a rational and logical conclusion. Now there's a religion with self-confidence. Don't have faith, says the first of the Ten Commandments. Rather, examine the evidence and decide for yourself. We're confident of the conclusion you will come to.
But why all the fuss? Whether a person with faith or one with knowledge, don't both equally accept the existence of God?
The difference is quite significant. Firstly, knowledge, by nature, is more reliable than faith. Faith is an emotion. When stronger emotions come along - such as love or pain - you might just change your mind about what you believe in.
But more importantly, faith and knowledge produce very different relationships. Knowledge means there is a God even when you don't feel like dealing with Him. Faith is much more flexible. It's as strong, or as weak, as you feel the need for it to be. Knowledge is God in control of the human being. Faith is the human being in control of God.