Again, borrowing a friend's question. This was my response. I quite like it though my friend likes a noncommittal all-religions-are-the-same answer better. *shakes head in sadness at such illogicalness*
So here goes:
I will attempt the question... and most of my answer will be "stolen" from Frank Sheed's book "theology for beginners" because I like it a lot.
To understand why Jesus is the only way to heaven, we have to understand
0. What happens after we die
1. What Heaven is
2. How to get there
3. Why God didn't just make us able to go there in the first place.
4. How God fixed stuff.
5. Theology is fun, but what does this all mean for why Jesus is the O. N. L. Y way???
I'll add numbers as I think of things hence the odd numbering.
So, it would be a long explanation of what spirit is and is not, so I will suffice to say that Humans are unique creations of God. Humans are the only creatures made of both spirit and matter. When we die, our spirit is unable to control our body anymore and the common terminology is it "goes to Heaven (maybe by way of Purgatory) or Hell."
on to what heaven is: (quoting) "' Eye has not seen nor has ear heard, nor has it entered into the heart of man, what things God has prepared for those who love him.' So St. Paul tells the Corinthians, quoting Isaiah. Until we reach heaven, we shall not know what heaven is. But, in the inspired word of God, we are given glimpses. In heaven, we shall know God in a new way, and love him according to the new knowledge... St John says (1 Jn 3:2) " We shall see him as he is" And we remember our Lord saying of the angels (Mt. 18:10) 'They see the face of my heavenly Father continually." Seeing is the key to life in heaven... The Church has worked out for us a first beginning of the meaning of this. Here below we know God by the idea we have formed of Him. But in heaven, our seeing will be direct. The nearest we can think of this is to think of the idea we now have of God; then try to conceive of God himself taking the place of the idea."
(still quoting, on question 3... no, 2) "But observe that all this is based on doing something which by nature we cannot do. The natural powers of man's intellect fall short of seeing God direct by a double limitation: our natural way of knowing things is by ideas, and God, being infinite, can never be within the hold of our natural strength to love. Life in heaven requires powers which by nature we do not possess. We need supernatural life. This is sanctifying grace, which we can only get by God's gift to us, which we accept into our hearts. If we do not have it, then to heaven we cannot go because simply our spirit lacks the powers that living in heaven calls for."
(3 ish) The beginning of what is called Salvation History (or the answer to "why did Jesus have to come to save us?") is the fall of Adam. What's most important in Genesis is the metaphor of Everyman, Everywoman, Everysin. God created us originally with sanctifying grace, but man sinned disobeying a command of God. There is something in the solidarity of the whole human race clear to God but not to us, that he could so treat the race as one thing. Some involvement in the fate of others we take for granted, like a father making decisions for his family. We do not see a solidarity for all men whatsoever-- foreigners, the dead, the unborn. But no one of them is remote to the eye of God. God sees the whole race, every member of which he created, as one thing-- somewhat as we see a family as one thing. The number and variety of people of all time does not impede the vision of the eternal and omniscient God. We all have sinned individually, but we are involved as a race too. Because Adam broke the unity, his children were born members of a fallen race. A given man might be virtuous and gain sanctifying grace, but he was a virtuous member of a fallen race: a race to which heaven was closed. Only if the breach between his race and God could be healed could he attain his own destiny. "
I'll put this sentence in because i find it funny: "The race had been at one with God; the central problem was at-one-ment, a word whose meaning we disguise by pronouncing it atonement." :)
Why did God do what he did to save us, instead of something else? I don't know... long discussion. not really a good answer. it's easier to focus on what God did than what God might have done.
(4) If this were a history book, chronologically time where the human race lived without much knowledge of God would come. Satan was the prince the world obeyed. The next chapter, the beginning of redemption, came when God revealed himself to Abraham, and created the Chosen People who were told that the Messiah would come to them. With mixed success: by the time the Messiah was due to come, the Jews were unshakably monotheistic, but only rare ones grasped the essential nature of the kingdom the Savior was to found. The supreme truth about the Savior, for which the chosen people were wholly unprepared, was that he was God. God chose that the sin committed in human nature should be expiated in human nature. In Jesus, humanity gave its all: a total obedience as against the total disobedience of man's sin. But he who performed the act was God. Because he was truly man, his sacrifice was truly human, so that it could be set against the sin of the race. But because he was God, his act had an infinite value, by which it compensated, outweighed, not only all the sin men had ever committed, but all they ever could. That is why it is redemptive. Also, the resurrection and ascension have there place in redemption. Unless God approves and accepts the offering, all is in vain. In restoring Jesus to life, God gives the visible sign that the priest who offered his own body and blood in sacrifice was wholly pleasing to him. In the ascension, God shows visibly that he is taking to himself that which has been offered to him."
"The bible says its true" is vague. Here's a concrete answer:
(oh dear, quoting again... but I do love this book) "At the Last Supper Our Lord uttered the words which are at once the formula of our redemption, and the charter of his Church. 'I am the way and the truth and the life. No man comes unto the Father but by me'.
By asking if Jesus is the ONLY way to heaven, we wonder about other possibilities. Is it possible to gain sanctifying grace and go to heaven without ever hearing the name Jesus? Theoretically, yes. Is it very likely? hm... don't really think so. Has it happened? I don't know. The only way we are given to determine whether someone is in heaven or not is through the process of canonization. So its theoretically possible that some people in heaven aren't Catholic/Christian. We have no way to tell. They didn't get there from the original channels set up by Jesus and we have no way to tell from normal channels.
But even if they do get to heaven, never knowing the name of Jesus, it is still the same true God who gives sanctifying grace and it was still Jesus who redeemed the race to open heaven for them to get in. "It is in union with [Jesus], and only so, that men come to the everlasting union with God which is their destiny"
Jesus is the way, the truth, and the life. It is possible to follow a path that you don't know, but the way is still the way whether you know it or not.
However, the question of whether Jesus is the way is rather shallow. To steal from what i'm about to quote "The way is not the goal."
"Salvation is not handed to us on a dish; in no sense is it a laborsaving device. What Christ does for men is what men cannot do for themselves, not what they can; what they can, they should. To have found the way is not the end; it is the beginning. They way is not the goal. Only the goal is, for us, permanence; the way may be lost.
We might lose the way as we might lose any way, either by wandering from it through error, or by lacking the strength for the effort. Against the danger of losing the way we need truth. Against the danger of falling by the wayside we need life--the life of sanctifying grace.
Salvation then involves truth, life, and union with Jesus. Jesus says to the Apostles "Go and teach all nations; baptizing them in the name of the Father and of the Son and of the Holy Spirit; teaching them to observe all things whatsoever that I have commanded. And behold I am with you all days even to the end of the world." (Mt 28:19-20). Observe how closely this follows the great formula of the Last Supper- truth , life, union.
Truth: The Apostles are to teach. Jesus promised that the Holy Spirit would lead them into all truth by bringing to their minds all that Our Lord had told them. And they were to teach the great mass of truth to all nations.
Life: They were to baptize. To be born means being born into the life of this world. To be born again means to be born into a higher life. And these were the men to whom he had given other powers for the dispensing of life. They were to forgive sins (Jn 20:23); that is, to give back the life of grace to those who had lost it by sin. And they were to change bread and wine into his body and blood--the very food of our life (Jn 6:54).
Union: Jesus says it! "Behold I am with you all days even to the end of the world" Through the Apostles--and since it was to be until the world should end, through their successors--we were to find the truth, the life, the union by which we shall be saved. "
It is logical that Jesus is the way to Heaven
1: God Exists (which I hope you believe)
2: God is Trinity: Father, Son, and Holy Spirit
3: In some way, humanity broke from God
4: God wants us to be with him
5: the Son, Jesus, came to reunite humanity with God.
6: Jesus is the way to unity with God (heaven).
From a non-Christian standpoint, if you do not want to believe that Jesus is God or want to believe different things about the fundamental nature of God (solitary God, seeing yourself as God, or pantheistic). Go for it... but there can only be one truth. There is some pretty good evidence for Christianity. But if you search for the truth, you cannot blind yourself to thinking "oh, i already understand christianity." you could blind yourself to other religions i guess. but i think that most people blind themselves to christianity.
What's wrong with Jesus being the way to heaven? Do you personally want to turn from Jesus to something else and still want to be saved? Or do you have other people that you want in heaven with you who are not Christian? What harm is there in accepting Jesus? (other than the G. K. Chesterton quote: "Christianity has not been tried and found wanting; it has been found difficult, and not tried"
There is a truth. There is a moral law, just like there is a physical law. If you jump off a cliff because you are trying to show you don't believe in gravity, people will laugh. A certain amount of religion must be applied to science: it certainly is so for scientific atheists and atheist evolutionists. Also, a certain amount of rational, scientific rigour must be applied to your religion. Just because a religion says "All humans should be one and should love each other" is nice... but is not religion, it's philosophy. Religion is our relationship with God. If it is not rooted in truth, it is in vain and will begin to hurt our ability to be one with each other and will begin to hurt each other.