Al-Kitab deals with the Islamic Law (Islamic Sharia)
Al-Hikmah deals with Faith and Morality and their details.
Preamble deals with the epistemological basis which is used to study the sources of religion and reaching correct conclusion regarding the right interpretation of religion as a whole (like principles of understanding Quran, Sunnah and Hadith & the correct interpretation of religion).
From a Practical standpoint, one can start from Al-Kitab and then move to the preamble and then Al-Hikmah.
From an Academic Standpoint, one can start from Preamble and then move to Al-KItab and then Al-Hikmah.
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For easy access to these lectures along with some important explanation, you can use the following link:
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