What is the wisdom behind the existence of verses whose meaning is known only to Allah, or regarding whose interpretation scholars differ, even though the Qur'an is clear and detailed?

The Holy Quran is divided into muhkam (clear and decisive) and mutashabih (ambiguous). The muhkam is that which is clear and evident, while the mutashabih is that whose meaning may be hidden from some.

The ihkam (perfection/decisiveness) by which the entire Quran is described refers to its mastery and excellence in wording and meaning. Whereas the tashabuh (resemblance/consistency) by which the entire Quran is described refers to its consistency in perfection, harmony, and absence of contradiction. As for the ihkam that describes part of the Quran, it means clarity and obviousness. While the tashabuh that describes part of the Quran means the obscurity and ambiguity of its meaning.

Ambiguity (tashabuh) is of two types: 1. Real: That which none knows save Allah, such as the realities of Allah's attributes and matters of the Last Day. 2. Relative: That which is ambiguous to some people but not others, and those firm in knowledge can comprehend its meaning. There is nothing in the Quran whose meaning is absolutely unclear to everyone.