Our faith has always instructed it's membership that most all faiths contain bits, pieces and segments of truth for we all have much to learn from one another. The test is using the spirit of discernment to choose for oneself whether it be true or untrue. We must be open to new knowledge and ideas. Of course the Holy Bible is not complete for it was not written beginning to end in it's current form. It is a compilation of letters, addresses and records. It would be folly to believe that the "complete" word is contained within that sacred work. I am currently preparing a hub on this particular subject.
This is why I, personally, thirst for knowledge of what others believe. Together we may be perfected. To claim absolute salvation because of one's affiliation to an organization or system of belief is prideful and will lead you on a damaging path. Exactly like a compass. You may wonder off course a little bit but at the end your destination has become way off track. This mindset is, in essence, tunnel vision and prevents you from seeing beyond the walls you have set up for yourself.
Think of it this way. If the Almighty didn't approve of variety we would not exist as individual human beings with our own mind, heart soul and most of all - liberty to choose...