Muslims, Hinduisms, Catholic, Mormons, etc. etc... Why are there several religions? since they all have the same objectives, and the same God. sometimes they fight, and even kill for their belief. why?!?!
As a Hindu we are taught that God is big and vast. It is taught that there are so many religions because every person experiences God differently. These experiences, along with differing desired spiritual goals, are the main reason why there are so many religions.
There is a simple story told about four blind men who walk in a forest. Each of them comes across an elephant, briefly. One touches the trunk of the elephant, another only its ear. Another man touches the tail, and the fourth one touches the body. Each of these four men have had an individual encounter with an elephant. Each of them was only able to touch a part of the elephant for the brief time the elephant was passing. To each of them an elephant is a very different thing. The meaning is that God is like the elephant. He is big and when we reach to touch God, we can only touch a small part. There are different religions because each of us is touching a different part of the elephant, each religion has touched a different part of God. Religions don't all necessarily have the same goals, either. Yes they want to promote peace and unity, but think for a moment....some want to go to Heaven and be with their personalize manifested experience of God, like Jesus, Krishna. Some people want to just see their family and ancestors in Heaven and some want to experience the paradise of Heaven. Some aren't reaching for Heaven at all, but merely finding peace right now in this life and experiencing God right now, in this moment and not concerned with a future. These are all very different spiritual goals, all touching different parts of God. God manifested to them in various different ways and thus we react to the experiences that those manifestations bring.
Why do religions fight? It is usually over not being respectful of other's experiences and trying to force others to experience what they experience. Sometimes conflicts aren't even really about religion at all, but since religion is expressions of our deepest Self, these conflicts begin to get expressed by us in the only way we can understand such things, through our religion.