If you read it carefully, the Bible does not actually say that only Christians will have eternal life in Heaven.
Jesus is the only way to the Father, but this does not tell us that we must be a Christian to go to the Father. It only tells us that those who go to the Father, will go there because of Christ.
According to John 3:16 we must believe in the Son of God to have everlasting life, but as Jordan Peterson might say, “what do you mean by God, and what do you mean by believe?”
Christians assume that a person must believe in Christianity. There must be repentance, but there must also be agreement with fundamental beliefs of the church.
A person who believes in a particular philosophy might say that they believe in the philosopher who developed the philosophy, The wife of the philosopher may say that she believes in him. Her statement of belief is a greater truth than the statements made by those who only believe in his philosophy. To truly believe in God, we should believe in who God is.
We see this very idea, two verses after John 3:16.
We must believe in the name of the Son of God. Surely that doesn’t simply mean believing in the name “Jesus”.
A person’s name represents their essence. When a person is somehow transformed, they will sometimes change their name because they are now a different person.
God is absolute Righteousness greater than we can comprehend.
To believe in the name of God, we must believe in the essence of God which is righteousness. All good people believe in righteousness. That is what it means to be a good person. Perhaps that includes everyone, perhaps not, but all good people will have eternal life in Heaven because they believe in the name of the Son of God.
Saved from what? In the Bible, being saved often referred to being saved from something in this life.
Jesus healed a blind man and told him that his faith had saved him, but the blind man was saved from a life of blindness. Every time the Bible talks of heaven, hell, judgment, or being saved it may be referring to judgment in this life which is called temporal judgment.
There are many interpretations of the Bible, all with some degree of Biblical support. It is noteworthy that the Bible can be interpreted to mean that Jesus will give eternal life to all good people on the Day of Judgment while our words and actions may still affect us in temporal judgment.
Temporal judgment, heaven in this life, is for the living not the dead.
Repentance has to do with the kingdom of heaven, which is at hand, which is temporal judgment. Eternal Heaven is entirely a gift of Christ for all good people.