Why are the Qur'anic directives not clear?
Why are the ehkaam (injunctions) in the Quran ambiguous and why did Allah leave it to us to interpret it in our own capacity? To take a small example, some people believe that it is okay for a male or a female Muslim to marry a person from the other faith, as long as they are Ahl-e-kitaab (people of the book). Some believe that only males are allowed that possibility. It is a small example but I wonder what was the need of making it ambiguous. Why not clarify it so that there is no confusion? There are many other instances like that.
The Almighty has made His law brief, simple, and clear. There is nothing ambiguous in it. However, when it comes to application, some situations become complicated. He wants us to make our own good judgment so that our devotion and sincerity are tested. Had He mentioned everything in detail, it would have made the law very detailed and restrictive; plus it wouldn't have tested our sincerity. We would, in that case, have been spoon-fed. The Almighty wants us to use our brains and apply ourselves to know what the best possible interpretation of a certain Qur'anic passage is. The Qur'an says: "Likewise has Allah clarified the verses for you so that you may reflect in the matters of worldly and other-worldly matters." (2:219-220) In the pursuit of this understanding, God Almighty doesn't expect from us anything except what is possible for us to achieve. "Indeed those who believe and do good deeds -- We shall not make anyone responsible for anything more than his potential -- such are the people of the paradise; they'll abide therein forever." (7:42)
The example of marrying people from other faiths is just one such instance of such a possibility.