What is the wisdom behind the Qur'an mentioning the period of creation of the heavens and the earth in six days, while it does not mention the number of obligatory prayers, and which of the two is more important for the worshippers to know?

Not everything mentioned in the Holy Quran is more important than what has been established in the Prophetic Sunnah, because both are revelations from Allah. The Prophetic Sunnah clarifies and elaborates on the Holy Quran. The Quran's silence regarding the number of rak'ahs for the obligatory prayers reinforces the importance of the Prophetic Sunnah, indicating that it is the second part of the revelation sent down to Prophet Muhammad, peace and blessings be upon him, and serves as proof of its authority. The rulings of Islamic law are either comprehensible in meaning and their wisdom discernible, or they are devotional (ta'abbudi) whose wisdom is not fully grasped but serve as a test for the believer. Human intellects have limitations in comprehending divine wisdom, and questioning rulings whose wisdom has not been understood contradicts faith.