I used to be fond of the phrase, "as long as you are a good person." For years this phrase summed up my world view as it pertained to religions. I once believed that it was not which particular religion you adhered to that made the difference, but it was whether or not you adhered to it at all. I used to believe that all faiths led to a common endpoint.
Perhaps expressed as a diagram, I imagined the world's faiths as spokes on a wheel like the diagram below. Imagine that each of the spokes is an arrow pointing toward the wheel's center. Similarly, I once believed that just as each of these spokes connects to the center, so too did the world's faiths reach God and God's pleasure and acceptance. Each reaches the goal but from a different angle, a different path. Each one had it's role to play.
While I still believe that it is important to be a good, kindhearted person, I have come to realize that there is a fundamental flaw in thinking that all religions lead to God's pleasure - that is, all religions as they are today. The most glaring flaw becomes evident when one examines contradictory beliefs. And perhaps the best example of this is the status of Jesus (peace be upon him). In the above model, how can it be that a path that elevates Jesus to divinity earns God's acceptance just as a faith that rejects Jesus and in some instances slanders his mother's name and calls Jesus a liar?
Another point that concerned me was that each of these faiths claims to be the right way. Although Islam, too, claims to be the right way, it is Islam that provides the only viable explanation of how and why different faiths exist, why each one claims to be correct, and how to discern the truth between them.
Islam says that God's religion or prescribed way of life is essentially one true, straight path. Throughout history God, in His Divine Mercy, sent prophets and messengers to call humanity to this straight way. The core message of the prophets was and is essentially the same message - God is One, God is the only One worthy of worship, obey your parents, help those in need, establish prayer, give in charity, etc.
With time, however, people would stray from that straight way by either adding to or taking away from the message. The reasons behind the initial straying may have been worldly in nature - racist, economic, sexist or political. Others may have been out of ignorance, say by adding one's cultural celebrations to the religious practice. And still others may have been with sincere intentions by, say altering one's religious practice or an element of faith to make it more palatable to the masses. See the diagram below
So, when a people or a nation strayed from a particular prophet's message, God would send another prophet to call them back to the straight path that all of the preceding prophet's called to. Those who rejected the latest prophet's message stayed on their erroneous ways. These erroneous ways may or may not have remnants of the original message. So, the world's faiths have some similarities - not because one borrowed from another. They have similarities because in some cases - certainly Judaism, Christianity, and Islam - their source was the same. But, those who find themselves on a path other than what the prophets called to, are on one of these strayings. And in examining the message of the Final Prophet, Muhammad (peace be upon all of the prophets), one will be looking at the final call to this one way that all of the prophets called to - Submission to God.