what is obligatory and recommended.

All praise is due to Allah, who sent among us a Messenger from our own people, reciting His verses to us, purifying us, and teaching us the Book as an explanation of all things, and as guidance, mercy, and glad tidings for Muslims:

“This is not a fabricated account, but a confirmation of what came before it, a detailed explanation of all things, and guidance and mercy for people who believe.”
Yūsuf: 111.

Only someone deficient in understanding and listening supposes that the Book and the wisdom do not provide clarification. Such a person shares something of the condition described by the people of the Fire when they say:

“If only we had listened or used our reason, we would not be among the companions of the Blaze.”
Al-Mulk: 10.

Yet this is common among many philosophers and speculative theologians, as well as ignorant practitioners of hadith, jurisprudence, and Sufism.

[Proofs for these matters]

As for the second category—the proofs for these foundational matters—some speculative theologians and philosophers suppose that revelation provides evidence only through truthful reports, so that its evidentiary force depends upon knowing the truthfulness of the one conveying them. They regard the grounds for establishing his truthfulness as purely rational considerations. In this they have made a grievous error; indeed, they have gone clearly astray in supposing that the Book and the Sunnah provide evidence only through reports alone.

Rather, the truth is what the early generations of this community, the people of knowledge and faith, held: Allah, glorified and exalted, has explained the rational proofs needed to attain knowledge of these matters to an extent that none of these people can properly appreciate. The Quran presents the essence of the most that they can offer, in the finest possible manner.