Why do Christians insist that theirs is the only way to Heaven? Humans have a deep desire to be loved and live in a loving, peaceful community. This desire is unlikely to be the product of the tooth and claw of evolution, the aggressive brutality of Islam, the indifference of karma, the legalism of Judaism, or the futility and purposelessness of atheism.
It could only be product of a God who would give up his place in heaven to live among us and die to redeem us from a life of futility and eternal death. He created us with a deep desire to love and be loved and he fulfilled that desire by loving us and giving himself to us. Though he was rich, he became poor that we might become rich, though he was the creator of life, he submitted to death that we might live forever, though he was the Son of God he became a son of man in order that men might become eternal sons of God.
He expects nothing from us except the humility and courage to admit that he is the one we have longed for all our lives. If you always had a sneaking suspicion that there had to be a God like him it’s because he made you that way. He did that so that you might seek him and find him and in finding him might find the source of everything you were created for.
No other god has died for you so no other God has the right to your love and devotion. That’s just one of many reasons we believe there could be no other way.