How can the Hadiths of the Prophet, peace be upon him, be speculative in terms of authenticity and indication while they are revelation like the Quran and clear in meaning understood by everyone? And what is the opinion of scholars and the ruling on acting upon them?

Praise be to Allah, the Sunnah (definition), revelation from heaven preserved by the protection of Allah Almighty, but it is not in the same degree of certainty and indication. Some of the Sunnah is definitive in indication, bearing only one meaning, and some bear more than one meaning, as in the Noble Qur'an. In terms of certainty, some are Mutawatir, definitively established, and some are Ahad, and they must be acted upon in beliefs and acts of worship.