Well, there is a difference between how people speak and how things are written even to this day - the news (al-Jazeera etc.) for example speaks the standard/formal Arabic like is written so that Arabs from Morocco to Iraq and even East Africans can understand it - yet if you put an Iraqi, Moroccan and Lebanese person in a room their dialects would be confusing... They would speak the standard to each other anyway.
If you are wanting to move towards Islamic studies and also have conversational ability, then I recommend something like Al-Kitaab that I linked above or any other text which teaches the standard. The main grammar and morphology etc. is essentially the same and so are the meanings of vocabulary although many have modern meanings.
Eg.
هاتف "hatif" - means telephone in Modern Standard Arabic, but means a disembodied voice - a voice you can hear but not see where from - in Classical Arabic. Which if you think about it, is what a telephone call actually is!
There are good texts like Haywood's well-known (but old)
A New Arabic Grammar of the Written Language, which has a good sample of literature from classical to modern times. But to be frank, it is very tedious and boring stuff to go through - something with speaking, listening and so on is much more interesting and interactive.
As my teacher explained to me - don't put being able to converse etc. down - the dialects are still Arabic and many things are actually from solid classical/standard Arabic words just with an accent. Eg. you will find in Lebanese/Syrian (and elsewhere) people refer to work as
شغل "shughl", whereas in the Standard we are taught
عمل "`amal" so might wonder why. Yet as our exposure grows, we find `amal means to engage in something/perform an action, whereas shughl means to be kept busy with something or to be occupied with something. So both basically make perfect sense in that context, in the spoken one is just used more commonly then the other.
Being able to converse/think in Arabic will bring up your understanding of the things you read - whether Qur'an or Islamic texts in general, or the likes of the Mu`allaqat, Imru al-Qays and other pre-Islamic epics... it just takes time to develop. Obviously being able to read and comprehend is different from being able to speak but it depends on your own self - how much you want to develop each side of things. The main thing is to be able to "think" in Arabic without having to always translate each sentence or passage in to English in order to understand it - which takes time - I am pretty much at the line between the two now after three years study at University although nowhere near fluent yet.
For me, although my main interest is reading for research, texts which develop the four key areas: Reading, Writing, Listening and Speaking get the thumbs up from me because I also want to be able to speak as much as possible - Arabic is an oral language after all.
The main thing that I always keep in mind is that Arabic is one of the few living languages left - we can see pre-Islamic poetry today from before or just after the time of the Prophet (saw) and anyone who is well-educated in Arabic today can read them and understand them at various levels depending on their experience and knowledge of the language. It is an amazing thing when you think about it!
dawood