What is the most critical factor in the determination of the quality of our experience? What makes life worth living, or suicide worth considering? What enables people to live in arrogance, despair, or fullness of joy? What decides what happens to a person once his/her physical body ceases to function? What makes physical pain tolerable or intolerable? What decides which relationships we have will succeed and which will fail? What determines whether we will have a sense of significance, or a sense of worthlessness?
Some would mistakenly answer "faith". It is, these would say, the lowest common denominator in all of the questions above. What a person believes determines the quality of experience; it makes life worth living or suicide worth considering; it enables people to live with an attitude; it determines what happens to a person when he dies... etc.
However, there is something even more basic than belief: Truth. Reality is. Faith can be misplaced, but reality is. The main problem with faith is that it can be completely in error and yet not be shown to be misplaced until it has caused an irreversible consequence. Many things about belief systems can be shown to be true or false by experience. But there are many things that are believed by many people that only the final experience of death and discovery of what is beyond the grave can correct...unless, of course, a person is willing to be corrected by the legitimate testimony of God's Word.
Let me illustrate. In the dogma of a supposedly infallible church there is a teaching that every Christian goes to Purgatory at death. There is absolutely nothing in the sacred Scriptures that substantiates this claim. Jesus said absolutely nothing about any Purgatory. None of the prophets and apostles who authored Holy Scripture ever said anything at all about any Purgatory. Even the catechism books of this church admit that the Bible has nothing to say about this ancient Jewish doctrine. And yet millions of people have believed in Purgatory.
What is going to determine if this is a misplaced faith or an accurate description of unseen reality? There are only two things that can reveal this: 1) ultimate experience (a person can die and see if Purgatory is real); or 2) legitimate testimony (a person who has been on the other side can come back, substantiate his claim of having legitimate experience on the other side, and then tell us what he found out). Now, Jesus, Lazarus, Paul, and a very few others had this experience of going beyond this world. None of them told us that Purgatory is real.
What difference does it make? A very great deal. Those who believe in Purgatory don't go to heaven when they die. If their belief in Purgatory is correct, when they die that's where they go. If their belief is false, they suffer the consequences of having believed a lie. Either way, they don't go to heaven. Does this affect their experience? Eternally. You see, God holds every individual personally responsible for what he believes. The deceived suffer from their willingness to be such because He has given us His Word. We ignore it at our peril.