If the answers in the Bible were so "clear," there wouldn't be 40,000 denominations and thousands of theological opinions, would there?
40,000 denominations =/= 40,000 theological differences
https://en.wikipedia.org/wiki/List_of_Christian_denominations
If you go to the Catholic section of that Wikipedia page, it lists a good 26 organisations which agree with each other
completely on matters of doctrine. The difference is in their various traditions and the liturgy, which are about how they practise their faith and what the church service looks and feels like.
The Orthodox section lists a similar number, which also agree with each other on doctrine but have regional differences in their traditions and liturgies.
Just going to the Anglican, Reformed and Lutheran sections and you see them list many many churches, which in actual fact will have very similar if not identical doctrine. (Although there are a few churches that have now opened their doors to gay marriages so the unity isn't all there, but for the most part the churches listed will have the same doctrine.)
Often you'll have a denomination that simply isn't worldwide, they will be in one country even though they may very well completely agree with another denomination across the world in matters of doctrine.
Honestly I don't know what an exact estimate of the number would be, but the 40,000 is a gross exaggeration which includes regional and non-doctrinal differences. Imagine every country has their own country-specific denominations, and the number can soon get quite out of hand.
If you just look at the Wikipedia page's headings, it divides the groups into major subdivisions, this is where the major doctrinal differences actually come into play. In this case, it seems likely there are under 100 real divisions of Christianity, perhaps as small as 50, but if we want to be generous I wouldn't say over 500, maybe 1000 at a huge stretch with various small fringe groups. In terms of major groups which actually make up a significant proportion of Christians, it's less than 50.