This is one of the classic objections to the Christian gospel. John 14:1-7 helps us to answer that question and show why Jesus must be the only way.
The context is Jesus’ last supper. Jesus has told his disciples that he is going to a place that they cannot come yet. Understandably they are distressed at this. Does it mean that Jesus is deserting them? Jesus responds by reassuring them, they do not need to worry, they can trust God, Jesus is going ahead to prepare for them and will return to them. He tells them that they know they way to which Thomas responds that they do not know the way, or where he is going. Jesus answers:
6 “I am the way, and the truth, and the life. No one comes to the Father except through me. 7 If you had known me, you would have known my Father also.[d] From now on you do know him and have seen him.”
Why does it matter that we say Jesus is the only way? Well it’s because he is the Son. As the Son, he reveals exactly what God is like, we are introduced to his character as a loving heavenly father. Without that revelation we are left with just an abstract notion of God. In fact, it is not just that we don’t know if any of the routes will lead us to God, we don’t even know if the God we will meet will be one we want to meet.
Certainly my own experience of all routes ending up at the same destination is when reading one of those choose your own adventure books from the 80s that always ended in an untimely and gruesome death or one of those nightmares where whichever route I take I always end up back at the same point face to face with my lurking fear.
So, before we set off down one of these paths to meet God, we don’t just want to be sure that the path takes us to God but that the god at the end of the path is one I want to meet. For example, many Eastern religious pathways take us to a divine entity which is impersonal. The goal of such religion is for us to reach the stage where we become pure spirit and are merged back into the divine losing all consciousness and personality. Nirvana is a far cry from the true paradise of an ongoing existence experiencing joy in the presence of God.
Through Jesus, we know specifically that God is good and loving, that he is gracious and that he is kind and that he invites us into his family. It is only through Jesus that we can know the destination into the arms of this good father.
Secondly, it matters because the way Jesus is talking about is through his death and resurrection. Now, if there were other ways that did not involve his death, If we can get to God by pilgrimages, obeying Torah, doing penance or transcendental meditation then that makes Jesus’ death cruelly unnecessary.
To claim that we can get to God through any route is to say that Jesus’ death and resurrection were worthless. It is to reject and dishonour the Son.
The only way to God is through Jesus because the loving Son reveals to us the good Father. The only way to God is through Jesus and that is why his death was necessary.