John 3:16 says: "For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.

John tells us we only have to "believe" in Jesus as our Saviour, but what does that actually mean? The word "believe" is not a simple profession, in this verse. Believe is an action word. I believe in Christ, but it gets me nowhere unless I am willing to act upon it. As children we "believe" it when our parents say the stove is hot, but there is something inside of us that makes us
want to see for ourselves.
(personal experience)
As Christians, we must be able to withstand that temptation to "see for ourselves." We must act on God's word and adhere to His laws. Then we will reap the benefits and rewards He promises.
II.
You must believe the Bible. You must without a shadow of a doubt believe every single word in the Bible to be true. You must also believe that it comes from God. A faithful person (in the Christian sense) does not separate any verse in the Bible and call it false. The entire Bible is complete and true, and it needs nothing added to it. This is what having faith in the Bible means.

The church of Jesus Christ of Latter Day Saints believe in a book of mormons. This book is an addition to the Bible (in their belief). A truly faithful Christian sees no truth in adding anything to the Bible. "Mormons" do not believe the Bible entirely even though they say they do. So, even though they claim to be, they ARE NOT CHRISTIANS!

Christians agree with the word of God totally. Jehovah's Witness, Mormons, Muslims, Jews, all of these, do not agree with the word of God totally. Therefore, they do not have Christian Faith.

Why Have Faith?
We must have faith. To the thinking man, Christianity may very easily seem
absurd. When, on the contrary, it is the most
logical belief out there. Many times
I hear, "Prove it to me!"
Christianity Cannot be PROVEN. As mentioned above we see that it is based on FAITH....faith is belief in the unseen. Belief in the unproven.
On the level of comprehension that I am capable of, Christianity cannot be proven. Many people turn away from Christianity because of this. It must be taken on FAITH, though. God planned it this way. Anyone would jump on an opportunity to live eternally in bliss, if they could prove without a doubt that it would happen. God wants us to trust Him. He made it easy, but we must have faith in His word to reap the rewards.
Jesus Christ DID die on a cross to save us from our sins. Will you believe and live out the faith or simply be closed minded because it can't be proven outright?